220 BECKETT ESTIMATION OF NITROGEN IN NITROCELLULOSE

XXVI1I.-The Estirrmtion of Nitrogen in Nitrocdulose and Inorganic N i t ra tes with the Nitwmeter.

By ERNEST GEORGE BECKETT.

THE estimation of nitroge'n in inorganic and organic nitrates by means of the nitrometer is based on the react,ion which occurs when a solution of the nitrate in concent'rateld sulphuric acid is shaken with mercury. This reaction may be, represented by the following equation :

3H2S04 + 2HN0, + 6Hg = 3Hg2S04 + 2NO + 4H20. The volume of nitric oxide evolved according to this equation

is a measure of the quantity of nitrogen preaent as nitrate, and it is assumed for the purpose of calculation that the gas obtained is pure nitric oxide5 and that all, and only the nitrogen present as nitrate, or nitrite, has been converted into gas.

It has been known for some time that these, assumptions are not correct, and hence, if the method givea trustworthy results, i t can only be by a compensation of errors. Several factors have, been found to exercise considerable influence on the course of the reac-

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AND INORGANIC NITRATES WITH THE NITROMETER. 221

tion, and thus it is essential that the method should be standardiseld as far as possible. Thus Marqueyrol and Florentin (Bull. SOC. chim., 1911, [iv], 9, 234> found that prolonged shaking causes a diminution of volume by reduction of the nitric oxide gas, and also a rel-absorption of some of the nitrogen by the sulphuric acid. This cause of error becomes negligible if the shaking is not unduly prolonged and i f the concentration of the acid is not too high.

This reaction also occurs i f the nitrometer is allowed to stand after the evolution of gas has taken place, but in that case' the reaction is very slow. In an experiment with guncotton and 96.8 per cent. acid, the original volume of 109.95 C.C. became 109.80 C.C. afte'r standing for twenty-six and a-half ho'urs. On the ot'her hand, the time which elapses before the mixture of mercury, sulphuric acid, and nitrocellulose has been shaken, but after the two latter substances have been introduced into the nitrometer, was found t o have a marked influence on the results: This fact was discovered in the analytical laboratory of Messrs. Nobel's explosives factory a t Ardeer in 1914, when the war caused a large increase in the number of nitrocelluloses to be analysed, and thus rendered almost unavoidable a certain amount of delay in carry- ing out the analyses.

Table I shows the influence of the time factor and of the con- centration of the1 acid on the results a t this stage of the method.

TABLE I. Octerminution. of iaitrogen in. guncotton, vlitli various strengths

of sulplhuric acid and t k e effect of a110?~i?zg t h e mixture to stand before beiny shaken.

Interval between introducing the guncotton and acid into the nitrometer and shaking being Sulphuric

Per cent. No time. 4 hour. 3 hour. 1 hour. 17-20 hours. acid. \

99.87 12.63 - - 11.76 - 12-50 - - 11.82 -

96.80 12-94 - - 12.74 10-14 12.945 - - 12.68 10.28

- 10.71 12.93 12.96

94.0 12.975 13.065 - 13.04 11.90

92.5 12-73 13.04 13.035 13.015 12.69

- - - - - _-

- - - - 12.57

The influence of the same factors on tlhe estimation of nitric acid is given in table 11. The results given in this table with 93.3 per cent. acid wore obtained with pure sodium nitrate, and those with

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222 BECKETT : ESTIMATION O F NITROGEN I N NITROCELLULOSE

the more concentrated acid with a mixture! of nitrio and sulphuric acids.

TABLE 11.

Determina t ion of n i t rogen in n i t r i c acid with various s t reug ths of szdphuric acid and t h e effect of nllouliiig t h e mixtzwe t o stand in the n i t r o m e t e r before being shaken .

Sulphuric acid.

Per cent. No time. 1 hour. 17 hours. 99-87 2.081 2.058 1.948

Interval between introducing the mixturo into the nitrometer and shaking being - /__-I____ ----

- - 2.098

16.38 16-32 - 93.3 16.38 16.32 16.398

The results of both tables are shown graphially in Fig. 1. It will be noticed that the effect of time and concentration of acid

13.1 %

8

u Y

b 12.9 LI1

11.7

Interval between introducing guncotton and acid into nitrometer and shaking.

was much less in the absence1 of organic matlter, but tlhhe influence of allowing the mixture t o remain, even with 93.3 per cent. acid, is quit8@ noticeable, and that with the stronger acid is quite markeld.

Marquerol and Florentin found that the highest, figures were obtained with 94 per cent. acid, but this result was not confirmed by elxperiments (not published) carried out, by chemists in ex- plosives works. It was generally found that 96-97 per cent. acid

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AND INORGANIC NITRATES WITH THE NITROMETER. 223

gavel the highest! results, and thus it camel about that this strength of acid is that most geimrally used for nitrometer work.

Neither Marquerol and Florentin nor the other chemists who investigated the question were apparently aware of the importance of the, time which elapses between the introduction of the guncottoii into the, nitrometer and the shaking, and the discrepancies in the results may be accounted for by this.

Tablet I shows that, the highest figures were obtained with the weaker acids, but only if a sufficient interval was allowed to elapse before shaking. If the nitrometer was shaken immediately after the guncotton was introduced, higher results were obt'ained with 96.8 per cent. acid than with 92.5 per cent. acid.

It is clear from these1 results that it. is preferable to work with a weaker acid, as the results are less influenced by the time factor than they are with the stronger acid; but the most, important question is to determine which results represent most closely the true nitrogen contlent.

Marqueyrol and Florentin, by comparing the nitrometer method with Schloesing's method, found that the former gavel correct results, but itl is unsafe to1 determine the trustworthiness of one method by comparison with another elqually unproven method.

I n a previous communication ( J . SOC. Ghem. Znd., 1914, 33, 628), the author attacked the problem in another way, and found that with guncotton and 96 per cent. acid the various errors balance one another, and that therefore the result\s were correct. This stateiment was supported by the analysis of the gas and the1 estim- ation of the nitrogen iii the sulphuric acid residues by Kjeldahl's method.

It has been found since that Kjeldahl's method in this case does not show all tlhe nitrogen-that some of the nitrogen in the residual sulphuric acid is not converted into' ammonia on heating, but is given off in the! form of nitrogen or nitrous oxide.

As the conclusion previously drawn must, have been wrong, owing to a part of the nitrogen having escaped detectiosn, it was decided to repeat the1 work on a more elaborate scale, and, so far as possible, to test every method of analysis employed with the view of dis- covering any source of loss.

This research deals principally with the estimation of nitrogen in nitrocelluloses, and the great, difficulty was the dete'rmination of the true nitrogen content. There is no method known of ascer- taining this simply and accurately. The method adopt.ed was the same as that used in the previons investigation, namely, (1) the analysis and measurement of the, gas e'volved; (2) the1 analysis of the sulphuric acid residues. As the nitrometer estimat<ion is carried

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224 BECKETT ESTIMATION OF NITROGEN IN NITROCELLULOSE

out in a closed glass vessel sealed by mercury, the1 nitrogen entering in the form of nitrocelluloses must, after the elxperiment, be! either in the gas or in the acid, as it may be taken for granted that, it cannot be absorbed in any quantity by the mercury. Besides the nitrogen introduced into the nitrometer as nitrocellulose, a small quantity ent'ers in the form of dissolved gaseous nitrogen in the sulphuric acid. If, then, the1 gas is accurately analysed and measured, and all the nitrogen in the sulphuric acid residue correctly estimated, the quantity of nitrogen in the nitrometes is correctly known, and by subtracting the nitrogen introduced by the sulphuric acid, the actual quantity of nitrogen in the nitro- cellulose can be calculated. This met'hod of proceldure has the advantage that the results show t o what the discrepancies in the ejstimation by the nit'rometer are1 due'.

I n this paper, the methods adopted for the1 analysis of the gas and the residual acid are described in Par t I, and the actual experimental figurels obtained are1 given and discussed in Part' 11.

PART I.

Methods of Analpsis.

Anulysis and Measurement of the Gm.-The gas was t!ransferred from the nitrometer to a gas-analysing apparatus similar in prin- ciple to that recommended by Bone and Wheeler, but specially designed for the particular requirements of the casel. The gas may contain, besides a large quantity of nitric oxide, small quantities of sulphur dioxide, carbon dioxidel, nitrous oxide, nitrogen, and carbon monoxide. The analysis was carried out in the following order :

(1) Absorption of sulphur dioxide and carbon dioxide. (2) Absorption of nitric oxide. (3) Absorption of carbon monoxide. As the gas is evolved in the dry state in the nitrometer, it was

measured dry. Great difficulty was experienced in attempting t o do this a t first, but by washing t,he measuring vmsel before use with 75 per cent. sulphuric acid and leaving one or two drops of itl in the, vessel, the results became motre satisfactory. A more concen- trated sulphurio acid was not used, as nitric oxide reacts with concentrated sulphuric acid and melrcury, and a weaker acid could not be used, as the vapour t'ension becomes too high. The vapour pressure of 75 per cent. sulphuric acid being about 0.7 mm. a t the ordinary temperature, t!he true dry volume of the gas was taken as being 999/1000 of that measured. As the carbon dioxide and sulphur dioxide were absorbed by dry sodium hydroxide, t!he volume

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AND INORGANIC NITRATES WITH THE NITROMETER. 225

was also measured dry aft'er these gases had been eliminated. After absorption of the nitric oxide by ferrous chloride solution, the residual gas was measured wet, and as the volumes of gas dealt with a t this stage of the analysis were comparatively small, no appreciable error was incurred in neglecting the vapour tension. In order to avoid a constant, drying of the apparatus, one part was used exclusively for measuring thel dry gas and another part only f o r the latter portion of the analysis. The gas was first transferred from the nitrometer into a gas-me,asuring vessel, which was immersed in water, kept stirred by a stream of air being bubbled through it, and measured dry after having been brought t o atmo- spheric pressure.

Estimation of the Carhorn Dioxide and fhlphur Dioxide.-Owing to the possibility of carbon dioxide and sulphur dioxide being absorbed by the reagents used for eliminating the nit'ric oxide, these were1 estimated first. Alkali hydroxides are1 stated to react with nitric oxide, and this was found to be, indeed, the case with solid potassium hydroxide. Solid sodium hydroxide, however, was found t o have no influence, as the following figures show.

TABLE 111. ,9howineq the action of nitric oxide om potassizcm hydroxide.

Volume of gas at N.T.P. Difference

in C.C. in C.C.

After one hour over KOH ............ 109.22 1.14 After another hour over KOH the

latter having been moistened ...... 109.08 0.14 After another hour ..................... 108.59 0-49

9 9 9 9 ..................... 107.90 0.69 9 7 9 9 ..................... 107-22 0.68

The large diminution in volume which occurred at first was due to the preseace of carbon dioxide a i d sulphur dioxide in the gas. The gas was theln allowed to act on a stick of solid sodium hydroxide.

TABLE IV. Showing the action of nitric oxide o n sodium hydroxide.

at N.T.P. Difference in C.C. in C.C.

Original volume.. ......................... 110.36 -

Volume of gas

Original volume.. ......................... 107.1 1 - After one hour over NaOH ......... 107.09 0.02 After another hour over NaOH which

had been slightly moistened ...... 107.16 - 0.07 After another hour and a half ...... 107.13 0.03 After two hours over a stick of

calcium chloride ..................... 107.08 0.05

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226 BECKETT : ESTIMATION OF NITROGEN IN NITROCELLULOSE

In the actual analysis, the gas was allotwed to1 remain for two t80 three hours in contact with the stick of sodium hydroxide!. The latter was tested on several occasions for nitrites and nitrate's by Devarda's method, in order to ascertain if any nitrogen was abstracteld from the gas by this trelat3ment, but no appreciable quantity could be found.

Estimation of the Nitric Oxide.-The gas, after absorption of the carbon dioxide and sulphur dioxide, consisted mainly of nitric oxide, and contained also small quantities of carbon monoxide, nitropn, and nitrous oaide. The latter gas, owing to its great solubility in most solutions, gave much trouble, but a concentrated solution of ferrous chloride seemed to be specially suitetd for separating nitrous oxide from nitric oxide, as the solubility of the former gas in it was found t o be about 16 per celnt. at' the' ordinary telmperaturs. Altogether, 9 C.C. of ferrous chloride solution were generally useld for absorbing the nitric oxide, and this solutlosn could have absorbed 1.4 O.C. of nitrous oxidel. Undelr the condi- tions of the experiment, however, it was found by a trial with a synthetic mixture that not more than 0.34 C.C. was absosrbed during the analysis of a mixture containing 9 C.C. of nitrous oxide and 109 C.C. of nitric oxide. When the quantity of nitrous oxide was much smaller, as was usually the case, the loss must have been much less.

I n the actual analysis, the gas was treated with 7 C.C. of con- centrated ferrous chloride solution until no further diminution of volume occurmd. It was then treated with 0.5 to 0.75 C.C. of the same solution for one to two hours a t ordinary atmospheric pressurel. Very little diminution occurred as a rule during this last treatment. The gas was then immediately measured. Wash- ing with water is not permissible, as t>he solubility of nitrous oxids a t the ordinary temperature is about 80 per cent. by volume. It was found thatl even with the small quantities of gas usually dealt with a t this stage of the analysis, treatment with 2 O.C. of water caused a loss of 0.3 c.c., although the gas contaimd a large, propor- tion of nitrogen and its volume was only about 1 C.C.

Estimation of Carbon iWonoxide.-The solubility of nitrous oxide in ammoniacal cuprous chloride, was found to bet about 30 per cent. by volume, that is, .twice that in ferrous chloride. Motreover, tlreatment with ammoniacal cuprous chloride, has always to be followeld by a treatment with water o r dilute acid to absorb the ammonia l e f t in the gas. This dosuble treatment caused such an apprelciable loss of nitrous oxide that the usel of t,his absorbent for carbon monoxide had to be avoided. Acid cuprous chloride! was found to1 be no better.

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AND INORGANIC NITRATES WITH THE "I'ROMETER. 22'7

An attempt was made to analyse the mixture by keeping the gas over a heated mixture of copper oxide and copper. The carbon monoxide, would bet osidised to carbon dioxide, and the nitrous oxide reduced by the copper to nitrogen. This method was found to work quite well if thel gas was kept far half an hour in contact with the mixture at 2 5 0 O . One treatment was found t o be sufficietnt when the gas was poor in carbon monoxide', but when the1 latter was present to the extent of 50 per cent. or morel, two treatments were necessary.

The copper was prepared by precipitation from a solution oif copper chloride! with a rod of pure zinc. Copper sulphate could notl bel used for this purpose, as the product then contains small quantities of copper sulphidel. The, copper oxide was first prepared by igniting copper nitrate, but it was found that the ordinary copper oxide, as used for combustions, made by igniting copper wire(, was just as suitable.

A mixture1 of about equal parts of these two subst,ances was placed in a glass bulb having a little, more than twice the volume of the gas to be analysed, and the bulb connected to the gas- measuring apparatus by a glass capillary tubel and an indiarubber tube connexion. Before each experiment, a small piece1 of fresh filter paper was inserted in the1 capillary tlube to absorb any liquid which it was difficult otherwise to prelvent from being drawn into the bulb. The bulb and contents were then heated in an oil-bath to 250-280° and exhausteld. The gas to be analysed was admitted, heated for an hour, and pumped out again. The volume was then measured, the carbon dioxide absorbed, and the volume me8asurecl again. The diminution represented the, volume of carbon mon- oxide. As the proportion of the latter gas was small, by adopting the proceldure described, incomplete exhaustion of the bulb before the1 treatment had no effect on the, results, and even if a trace of the gas had been left in the bulb after treatment, the accuracy of the analysis was not appreciably impaired.

No attelmpt was made to ascertain the proportion of nitrous oxide to nitrogen in the nitrometer gas. They were both classed together, as they contain the same quantity of nitrogen per C.C.

Estimation of the Nitrogen in the Sulphum'c Acid Residues.

Zstimation of the Gases Evolved o n Heating.-A flask of the shape1 shown in Fig. 2 was filled with mercury, care being taken that 1101 air was left adhering to the sides of the1 vessel. It was then inverteld, with t,he end of the1 long tube dipping in a trough of mercury. By this means, a Torricellian vacuum was produced

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228 BECKETT : ESTIMATION OF NITROGEN IN NITROCELLULOSE

in the vwsel, which contained no appreciable quantities of permanent gas.

The sulphuric acid residue) was transfelrred from the nitrometer to the funnel, and alloweld to be drawn into the vessel, care being taken that no air was sucked in with ;%. The nitrometer was washed wit,h two quaiit'itiea oef 5 C.C. of sulphuric acid, which were also transferred to tlhe flask in the same way. The flask was gently heateld, as in a Kjeldahl estimation, and the sulphur dioxide pro- duced by the action of the mercury which had been left in the stopper of t'he apparatus and had been sucked in, togelther with

FIG. 2.

the sulphuric acid, swept out all the other gases in a comparatively short time. The gases were, collected ovelr 20 C.C. of a 30 per ce'nt. solution of poltassium hydroxide, and consisted in the case of gun- cotton mainly of carbon monoxide with a litth nitrogen and nitrous oxide. The aoid from an analysis of an inorganic sub- stance gave only nitrogen and nitrous oxide. It is curious that nitrio oxide was neiver found in t$hese gases in appreciable quanti- ties, although the sulphuric acid must have beleln saturateld with the gas when it was in the nitrometer. The mercury dissolved in the sulphuric aoid is in the form of mercurous sulphatei in the nitro- meter, but after the acid has been heated, the mercurous sulphate

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AND IRORGANIC NITRATES WITH THE NITROMETER. 229

is converted into mercuric sulphate. No doubt the nitric oxide is reduced a t t h s higher ternperatwe by the mercurous sulphate to nitrogen o r nitrous oxide.

After the evolution of gas had almost ceased, which occurred when the drop of mercury had dissolved, the sulphuric acid was heated to boiling until the liquid appeared transparent, but not necessarily colourless. Experiment showed that heating until colourless, and heating for several hours after the acid had become colourless and after the addition of potassium sulphate, had no effect on the amount of ammonia formed in the sulphuric acid.

The gas collected over the potassium hydroxide, which in the case of nitrocellulose usually amounted to 2 to 3 c.c., was trans- ferred to the wet gas analysis apparatus, and the carbon monoxide removed by heating over copper and copper oxide and treatment with sodium hydroxide. I n this case, where the quantity of carbon monoxide was very much greater than that of the nitrogen gases, the actual reaidue of nitrogen was measured, and not the diminu- tion in volume on treatment with potassium hydroxide, as described above.

Experiments were carried out in order to ascertain whether the 20 C.C. of potassium hydroxide dissolved an appreciable quantity of nitrous oxide, which would thus escape detection. A concen- trated sulphuric acid was prepared containing a known volume of dissolved nitrous oxide in solution. A weighed quantity of this acid was subjected to the same treatment as the sulphuric acid residues from the nitrometer estimations, and the volume of gas obtained was only 0.11 C.C. short of that which the acid contained. This experiment represents an extreme case, as the quantity of the gas was greater than that usually found, and it consisted of pure nitrous oxide, whereas in the actual analysis of nitrocellulose acid, the proportion of nitrous oxide in the gas must have been less than 25 per cent.

The potassium hydroxide after an experiment with nitrocellulose was examined for nitrates and nitrites by Devarda’s method, but none could be found. Blank experiments were always carried out with the same quantities of the same sulphuric acid as used in the actual analysis, and the results obtained in these really represent the quantity of gas dissolved in the sulphuric acid. In the blank experiments, however, the gas contained also a small quantity of oxygen, which had to be removed with alkaline pyrogallol solution.

Estimation of Ammonia formed in the Acid.-The sulphurio acid after it had been boiled until transparent was transferred to a round-bottomed litre flask, and after adding an excess of sodium

VOL. CIXVIT. K

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230 BECKETT ESTIMATION OF NITROGEN IN NITROCELLULOSE

hydroxide! and sufticient sodium sulphide to converb all the mercury present into sulphide, the ammonia was distilled off into a known quantity of N/lOO-acid. The acid was then titrated with N/100- sodium hydroxide.

Blank determinations were always carried out with the same quantities of the same sulphurio acid, sodium hydroxide, sodium sulphide, and water as in the actual analysis.

Many attempts were made here also to ascertain if any loss of nitrogen occurred.

The ammonia distillation was carried out with the addition of Devarda’s alloy and other reducing agents in a variety of ways without increasing the result.

The distillation of ammonia was also carried out under diminished prmsure, and the evolved gases were collected, but the quantity of gas so obtained, namely, 0.29 o.c., was not much greater than that given off in a blank determination, namely, 0.20 C.C.

The addition of sodium sulphide was found to be essential.

D ~ s m s i m of Results Obtctined.

The following are the details of the nitrometric method which was used for obtaining the results given in this paper. The method is similar to that used in many explosive factories.

The nitrometer was first washed out with concentrated sulphuric acid, and the cup washed with distilled water and dried.

Dried and sieved nitrocellulose (0.5-0.55 gram) was placed in 8 weighing bottle and heated to 96O in a steam-bath for one hour. The weighing bottle was then accurately weighed, the nitrocellulose dropped into the cup of the nitrometer, and the empty weighing bottle weighed again. Five C.C. of the sulphuric acid of specified strength were added to the cup, the nitrocellulose was stirred in the acid with a glass rod, and run into the nitrometer. The @up was then washed with successive quantities of 2.5 c.c., 2.5 c.c., and 5 C.C. of the same acid, and these were run into the nitrometer as well. The whole operation of washing the nitrocellulose into the nitrometer with the 15 C.C. of acid occupied five minutes. AfCer the introduction of the acid and nitrocellulose, the nitrometer ww allowed to stand for the specified time and then vigorously shaken for one and a-half minutes. It wils allowed to stand for ten minutes, again shaken vigorously for one minute, and the gas transferred to the measuring vessel described above.

The sodium nitrate was introduced into the nitrometer cup in

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TABLE V.

Giv

ing

anal

yses

of

the

va

riw

pro

duct

s of

n

itrm

ter

dete

rmin

atio

ns.

Inte

rval

be

twee

n in

trod

ucin

g gu

ncot

ton

Sul

- an

d ac

id

phur

ic

into

the

ac

id.

nitr

omet

er

Subs

tanc

e P

er

used

. ce

nt.

Dup

ont

high

ni

trog

en g

un-

96.8

co

tton

. ] 96.8

96

.8

Gun

cott.

on. ...

{ 96

.8

Hip

hly

solu

ble

(96.

8 m

troc

ellu

lose

. 19

6.8

Bla

etin

g so

lubl

e 96

-8

nitr

ocel

lulo

se.

{ 96.8

PUre

so

dium

19

6.8

nitr

ate

(Kah

l-

baum

).

196.

8

92.5

G

unco

tton

... 19

2.5

F: S

odiu

m n

itra

te

96.8

and

shak

ing.

Non

e N

one

Non

e N

one

Non

e N

one

Non

e N

one

Kon

c

Non

e

Non

e 80 h

ours

N

one

f hour

17 h

ours

X

one

17 h

ours

Ana

lysi

s of

gas.

Nh a

nd

stan

ce

CO

, and

N

. an

d ev

olve

d S

ub-

-I----'\

N,O

used

. N

O.

SO,.

CO

. h20.

Gra

ms.

c.

c C

.C.

C.C

. C

.C.

0.51

135

106.

76

0.50

965

106.

27

0.54

865

111.

81

0.52

63

107-

69

0.54

415

109.

03

0.53

9i.5

10

7.94

0.

9557

5 10

4.65

0.

5515

5 10

4.37

0.25

0.

30

0*64

* 0.

47'

0.2

1 0.

15

0.22

0.

22

0.25

0.

82

0.25

0.

85

0.23

0.

82

0.17

0.

80

0.16

0.

63

0.21

0.

66

0.26

0.

95

0.25

0.

73

0.45

13

117.

iO

0.11

-

0.48

0.50

0.

4526

6 11

8.09

0.

03 -

0-52

525

102-

23

1.10

0.

23

1.49

0-

5294

76

.43

2.29

1.

30

10.7

0 0.

5316

10

5.86

0.

26

0.08

0-

65

0.52

28

107.

72

0.66

0.

16

0.53

0.

4509

11

6.37

0.

20 -

0.98

2.86

7 95

.08

0.45

-

0.75

3.

140

91.7

9 2-

19 -

3.27

as gas.

0.59

0.

62

0.48

5 0.

50

0.58

0.

59

0.68

0.

635

0.35

C.C

.

0.40

0.72

2.

06

0-45

0.

38

0.67

1.

94

Ana

lysi

s of

b

N, i

n ca

lcul

ated

re

sidu

al a

cid.

N

itrog

en

NH.

acid

fr

om

f orm

e'd

in a

cid

NO

.

1-16

1-

20

1-20

1.

13

0.89

0.

94

1-16

1.

12

0.15

as C

.C.

0.08

47

5

8-83

3.

28

0.98

0.

27

0.07

1-

29

used

vo

lum

e fo

r of

cru

de

anal

ysis

. gas.

C.C

. Pe

r ce

nt.

0.39

13

.21

0.39

13

.196

0.

39

12.9

3 0.

39

12.9

6 0.

39

12-6

4 0.

39

12-6

2 0.

39

11.9

3 0.

39

11.9

65

0.39

I =':;3::% [

NaN

O,

0.39

[ =9%

48%

N

aNO

, 0.

62

12.5

0 0.

39

10.7

1

0.30

12

-57

0.30

13

.04

0.39

16

.30

0.62

-

0.62

-

16.3

82

Cor

rect

ion

to b

e ad

ded

to p

er-

Cor

rect

ed

cent

age

of

nitr

ogen

ni

trog

en

cont

ent

crud

e fr

om

Per

cent

. ga

s-

13.4

4 13

-45

13.0

85

13.1

4 12

-82

12.8

1 12

.18

12.1

8 16

.447

NaN

O,

16.4

59

NaN

O,.

13.1

15

12.9

13.1

4 16

.44

= 99

-90 %

=99*

97 %

-

0.23

0.25

5 0.

166

0.18

0.

18

0.19

0.

26

0.21

5

0.06

5

0-07

7

0.61

6 2.

19

0.10

0.

14

-c

* Ot,h

er re

aults

for

the

dete

rmin

atio

n of

car

bon

diox

ide

in t

he gas f

rom

gun

cott

on w

ere

also

obt

aine

d, b

ut t

hey

wor

e no

t ad

ded

fa t

he

tabl

e aa t

he a

naly

ses

wer

e no

t co

mpl

eted

. T

hese

res

ults

for

a s

imil

ar q

uant

ity

of gas w

ere

0.57

, 0.

57.

0.40

. 0.59.

0.56

C.C

.

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232 BECKETT : ESTIMATION OF NITROQEX IN NITROCELLULOSE

the same way as tbei guncotton, but it was then diwolved in two portions of water of 0.5 0.0. each, which were run into the nitro- meter, and the cup was washed with 96.8 per cent. sulphuric acid, as described above. I n this citse, the addition of the water reduced the concentration of the acid to 93.3 per cent.

The results are given in table V. The results for the various kinds of nitrocellulose under the same

conditions show that they act in the nitrometer in the same way under normal conditions with 96.8 per cent. acid; the only essential difference observed was the quantity of carbon dioxide and sulphur dioxide in the gas evolved from guncotton. This difference is not caused by any special behaviour of the guncotton itself, but by the presence of calcium carbonate, as the following figures show.

TABLE VI. Giving percentage of calcium carbonate in the nitroCeUutoses wed.

CaCO,. COzfrom 0.63 gram. Per cent. C.C.

0.29

0.07

Dupont high nitrogen guncotton ... 0.02 0.026 Guncotton . . . . . .... . . . . . . . . ... . . . . . . . . .. .. . Highly soluble nitrocellulose . . . . . . . . . 0.02 0.025 Blasting soluble nitrocellulose.. . . . . . . .

0.25

0.06

Taking the figures as EL whole, it will be seen that under all the condition8 examined, the results calculated from the crude gas with both inorganic and organic nitratea were too low. The beet result for guncotton was obtained with 92.5 per cent. acid and an interval of fifteen minutes between the introduction of the gun- cotton and acid into the nitrometer and the shaking. It will also be observed that the best results are concomitant with a high degree of purity of the gas and, a t the same time, a small content or" nitrogen in the residues. With guncotton, the purest gas is obtained with 92.5 per cent,. acid, and no interval between the introduction of the nitrocellulose and the shaking; but in this case a large amount of nitrogen is retained by the acid, due, apparently, to incomplete decomposition of the guncotton.

The table also shomws that the errors in the case of inorganic nitrates are smaller than they are with nitrocellulosm; hence the standardisation of the nitrometer with pure sodium or potassium nitrate does not necessarily eliminate the errors of the determin- ation of nitrogen in organic nitrates.

The use of the more dilute sulphuric acids is advisable, not only on account of the better results obtained, but also because they generally contain a smaller quantity of dissolved nitrogen.

Nitrogen appears to dissolve in a greater degree the' more con-

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AND INORGANIC NITRATES WITH THE NITROMETER. 233

centrated the acid between the limits of 90 and 100 per cent.; hence more dissolved nitrogen is usually found in the more highly concentrated acids, as the figures in table VII show. These figures have bean calcuIated from the blank experiments mentioned on p. 229.

TABLE VII.

Dissolved saitror~en in concentrated sulphuric acid.

Sulphuric acid. Percentage of nitrogen Per cent. by volume.

99.87 3.09 96.8 1.56 94.0 1-1 1 92.5 0.98

The nitrogen from the sulphuric acid is partly driven out during an estimation by the escaping nitrio oxide, and is thus partly responsible for tlhe content of nitrogen in the latter gas.

The separate atimation of nitrogen and nitrous oxide in the nitric oxide was not carried out in the above analyses, as these two gases contain the same quantity of nitrogen per C.C. In two cases, however, this was determined by combustion with hydrogen. The crude nitric oxide was obtained by shaking guncotton with 96 per cent. sulphuric acid, after allowing the mixture t o remain in the nitrometer for about twenty-four hours. In one case this gas contained 4.6 per cent. of nitrogen and 6.8 per cent. of nitrous oxide; in the other experiment, the gas was found to contain 5.8 per cent. of nitrogen and 5.6 per cent. of nitrous oxide.

The large quantity of gas evolved on heating the rwidual sulphuria acid in some of the experiments described in tlable V was explained by the great solubility of nitrous oxide in concentrated sulphuric acid, which was found t o be about 58 per cent. by volume a t the ordinary temperature.

Influence of the Quantity of Sdphuric Acid.

The question of the influence of the quantity of sulphuric acid used is of importance, as many firms, especially those in America, use 50 C.C. of 94-94.5 per cent. sulphuric acid and the Lunge volumenometer, instead of 15 C.C. as in the ordinary nitrometer. Apparently the larger quantity of acid is used to accelerate the decomposition, which with a smaller quantity of this strength of acid might remain incomplete unless a sufficient interval were allowed between the introduction of the guncotton and the shaking. The larger quantity of nitric oxide dissolved in the acid is corn-

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SSnb

stanc

e N

o. o

f us

ed.

expt

..

Gun

cott

on I3 M

ean.

Gw

ing

resd

ts obtained

TABL

E VII

I.

wit

h 50 C

.C. of 9

4 pe

r ce

nt.

dphw

ric

acid

.

Cru

de

Sub-

gas

at

stan

ce.

N.T

.P.

Gra

m.

C.C

.

0.52

53

108.

09

0.62

486

108.

06

0.52

546

108.

35

0.46

11

117.

52

0.44

97

116.

93

0.44

59

11 5.

87

0.44

975

117.

23

Xi t

roge

n ca

lcul

ated

N

itro

gen

Cor

rect

ed Corrected

8 fr

om

in a

cid

cont

ent

nitr

ogen

..

cr

ude

used f

or

of

nitr

ogen

con

tent

, ga$.

anal

ysis

C

ompo

siti

on of

C

ompo

siti

on of

ca

l. as

Per

P

er c

ent.

. C

.C.

acid

. C

.C.

NO

. ce

nt.

z F

rom

No.

2.

Fro

m N

o. 2

. P

12.8

6 1

/NO

=1

06

.48

~.~

. N, a

nd N

2O

ti^ g

~=

0*9

4

C0=

0.13

C.C

. N

O

pres

ent as

amm

onia

N, a

nd N

20

= 1.

13 C

.C.

= 1.

20 C

.C.

12-8

9

12.8

7 -

-

Fro

m N

o. 7

. N

O=

116-

50 C

.C.

- -

N, and N

,O =

0.89

C.C

. -

16-2

9

16.2

55

10.2

45

16-2

9

16.2

7

110.

40

13-1

6

1 J

-

13-1

5

Mea

n

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AND INORGANIC NITRATES WITH THE NITROMETER. 235

penaated by standardising the measuring apparatus with pure potassium nitrate. The results obtained with 50 C.C. of 94.0 per cent. acid are given in table VIII .

The results show that the ammonia formed in the residual acid is the same as with a smaller quantity of a similar acid, but that all the other sources of error are greater; hence the actual volume of gas obtained is smaller than with the ordinary nitrometer, and even standardisation with potassium or sodium nitrate does not produce, results any higher or truer than those obtainable with the ordinary nitrometer.

It may be mentioned here that in the experiments with sodium nitrate, the addition of 1 C.C. of water to 50 C.C. of 94 per cent. acid produced an acid of about 93 per cent., that is, practically the same as that obtained in the other experiments with sodium nitrate, where 15 C.U. of 96.8 per cent. acid were diluted with 1 C.O. of water.

Cmclztsim.

The general result of the research is that the nitrometric estim- ation of nitrogen in nitrocelluloses invariably gives reaults which are too low.

It has been found that the interval of time which is allowed tlo elapse between the introduction of the nitrate and sulphuric acid into the nitrometler and the shaking has a great influence on the results in the case of nitrocelluloses. The effect is less in the case of inorganic nitrates.

The truest results are obtained by using 15 C.O. of 92-5-94.0 per cent. sulphuric acid, and by allowing a quarter to half an hour to elapse betwejen the introduction of the nitrocellulose and acid into the nitrometer and the shaking. I n this case, the error is about 0.7 per cent., taking the nitrogen as 100.

This research was carried out in the Research Laboratories of Nobel’s Explosivee Co., Ardser, and I wish to express here my thanks to Mr. J. Rogers, O.B.E., and to Mr. W. Rintoul, 0.B E., for their kind permission to publish the results.

FALKIEK, STIBIJNQSHIRE . [Received, November loth, 19 19.1

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