541.3 : 541.12

ON THE INFLUENGE OF SOME NONINFLAMMABLE VAPOURS OF ORGANIC LIQUIDS ON THE LIMITS OF INFLAMMABILITY OF METHANE AIR MIXTURES, I1

BY

W. P. JORISSEN AND J. C. MEUWISSEN.

Recently one of us ') published the results of experiments made with Dr. Velisek, concerning the influence of some noninflammable vapours on the limits of explosibility of methane air mixtures.

The former*) had already made observations on the influence of carbon tetrachloride and trichlorethylene on the limits of explosibility of methane.

The results obtained with Dr. Velisek deviated from his. As this could be attributed to differences in method and differing purity of the substances (the methane for instance had been prepared from aluminium carbide with water), it was decided to repeat the experi- ments both with pure methane and with "technical" methane, and in the first place, with a view to practice, to study the influence exerted by carbon tetrachloride and trichlorethylene.

The apparatus chiefly resembled that described and reproduced in the former paper Also the burettes I and I11 were now provided with lateral tubes B with stopcocks. These not only made possible a quick and easy cleaning of the burettes by means of a current of air, but above all facilitated the mercury levels being brought to the same height in the gas burettes.

Three different explosion burettes were used. The upper parts of the burettes are shown in figure 1 (a, b and c). In burette a a rod s made of lead glass kept the platinum wires d immovable, in the others this rod proved not to be necessary. Burette c was provided with a lateral tube e which allowed mixtures of air and unsaturated vapour to enter.

Experiments were also made using a round bottomed vessel, capacity 1120 cc. (fig. 2). In the neck of the flask was inserted a rubber stopper with three holes through which a glass tube and two copper wires (3 mm. in diameter) passed. The ends of the wires just reached the centre of the flask and were 2.5 mm. apart. A pieceof ebonite served to hold the wires in place.

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I) Rec. trav. chim. 43, 80 119241. % ) Chem. Weekblad 18, 636 (1921).

Rec. trav. chim. 43. 84 !1924).

592

When performing the experiment the flask was evacuated : then stopcock 1 was closed and methane and air were introduced through

a 4f c

Fig. 1 .

stopcock 2 in the desired quantities. After waiting for half an hour the mixture was sparked in the same way as with the burettes4).

Experiments with pure methane. The pure methane (about 30 L.) had been prepared from methyliodide with magnesium and water The analysis of the gas proved the absence of carbon dioxide, oxygen and heavy hydrocarbons : therefore the gas could be con- sidered to be practically pure methane. The experiments mentioned here were all made with the same gas. The numbers give the proportion of methane in the mixtures of air and methane in volume per cent.

Burette b. Temperature 2OO.O. No explosion at 3.4 and 3.6: explosion at 3.8, 4.05, 4.5, 4.8, 5.0, 6.05, 10.0. 11.0, 11.4 and 11.5; no explosion at 11.6, 11.75, 12.0 and 12.4O/,. Limits of inflam- mability at 3.7 and 11.55 vol '/, of methane.

4, Rec. trav. chim. 43, 83. E. Schlumberger and W. Piotrowski, J. Gasbeleucht. 43, 941 11914,.

6) 40 gr. magnesium were introduced into a vessel of 1 liter capacity provided with a vertical condenser, dropping funnel and tube for the introduction of carbon dioxide. In an atmosphere of carbon dioxide, 50 cc. of a mixture of equal parts by volume of methyliodide and ether were added. As soon as the reaction began, the vessel was cooled in ice water and more ether was added : making in all 200 cc. After this another 150 cc. of the mixture, cooled in ice, was added: in all about 100 cc. of methyl- iodide i. e. about 230 gr. The vessel was heated at a temperature of 70° during an hour on a water-bath. The calcium chloride tube, which had been placed on the vertical condenser was now replaced by an inclined condenser and the ether distilled off as much as possible. The inclined condenser was again replaced by a series of 8 washing bottles of which one was empty, while two of them werefilledwithalcohol. or with water, two with a strong solution of caustic potash, and two with concentrated sulphuric acid. Water was now slowly dropped in the mixture in the vessel while the vertical condenser was cooled with ice water. Parts of the escaping gas were regularly analysed, and as soon as the gas proved to be free from oxygen, it was collected.

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6 :# I

>

594

Experiments with carbon tetrachloride and pure methane. The carbon tetrachloride had been purified by distillation ; boiling point (corrected) 76O.7-76O.9.

of vapour). No explosion at 5.05, 6.1 and 6.3; explosion at 6.5, 6.8, 7.5, 8.05, 8.6 and 8.8; no explosion at 9.1 and 9.4. The limits are consequently 6.4 and 8.95 vol. O/,,

of methane (calculated on the mixture of air, methane and vapour; in all the later experiments the same calculation was made).

Temperature 10O.1 (7.5 vol. of vapour). No explosion at 7.1 and 7.35; explosion at 7.5 and 8.0; no explosion at 8.3 and 8.5; the limits are therefore 7.4 and 8.15 Ole.

Temperature i1O.O (7.8 vol. of vapour). No explosion at 7.6; explosion at 7.8 ; no explosion at 8.0. This proportion of the carbon tetrachloride vapour therefore brings the limits practically together (fig. 3).

Experiments with carbon tetrachloride and technical methane. The first experiments were made, using commercial carbon tetrachloride.

Burette a. Temperature 15O.O (9.6d9.7 vol. O i , of vapour). No explosion at 8.65, 9.1, 9.3, 9.5, 9.8, 9.9 and 10.Oo/,.

Temperature 1 4 O . O (9.0 vol. of vapour). No explosion at 8.65, 9.0, 9.1, 9.25, 9.45, 9.5, 9.6, .9.9 and 10.2O/,.

Temperature 13O.O (8.5-8.7 vol of vapour). No explosion at 8.6, 8.9, 9.0, 9.2, 9.4 and 9.S0/,,.

Then the liquid was purified by distillation, bp. (corr.) 76O.7-76O.9. Temperature 13O.O (8.5-8.6 vol. of vapour). No explosion at

Temperature 10O.O (7.5 vol. o / o of vapour). No explosion at 8.3;

The limits practically coincide at 8.5 , lo . Temperature 8O.O (7.2 vol. vapour). No explosion at 6.0, 6.5,

7.0, 7.5 and 7.85. Explosion at 8.0, 8.1, 8.6, 8.9, 9.0, 9.5 and 9.6. No explosion at 9.8 and 10.Oo/o. Consequently the limits are 7.9 and 9.7 of methane.

Burette b. Temperature 7O.9 (7.2 vol.

8.0, 8.2, 8.6 and 9.O0/,.

explosion at 8.5; no explosion at 8.7.

Recapitulation. P u r e m e t h a n e .

Temp. Burette b Burette c Vessel

100.1 9 , 9 . 1,

110.0 .. ,, 9.

Limits of inflammability

# without vapour 3.7-1 1.55 4.9-1 2.6 5.15-13.65 7O.9 CC14. bp. 76O.7-76O.9 (7.2 VOI. 6.4- 8.95 - -

,, (7.5 ,, ,,) 7.4- 8.15 - - ,. (7.8 ., .,) 7.8 - -

T e c h n i c a l m e t h a n e . Limits of inflammability

Burette a Temp. without vapour 5.1 5-10.25 15O.O CC14 (commercial product) (9.6-9.7 vol. o/o) no explosion 14O.O .. .t ) ( 9.0 " .* ., 13O.O ,, ,. ) (8.5-8.7 ., ., ) ,, ,,

10O.O ,. ,, ( 7.5 9 . .. 8.5" 13O.O ,, bp. 76O.7-76O.9 (8.5-8.6 ,, ,,) ,,

8O.O ,. ,, ( 7.2 ,, ,, ) 7.9 - 9.7

595

Discussion of the results. It was already known and the preceding experiments show it again, that the limits of inflammability of methane are dependent on the nature of the vessel and also on the spark.

The influence of the vapour of carbon tetrachloride either on pure or on technical methane is practically the same. With pure methane the limits proved to coincide at about 7.8 vol. o / o of vapour and with technical methane at about 7.5 vol. O i 0 .

Dr. Velisek experimenting with the latter gas found that the limits nearly coincided at about 8.5 vol, O i 0 .

The carbon tetrachloride used by him was, however, another preparation.

In connection with these results the extinguishing power of air saturated with carbon tetrachloride vapour, on the flame of methane, was investigated.

A glass cylinder (length 33 cm. diameter 6.2 cm.; capacity about 1 liter) was placed in a thermostat. At different temperatures the air in the cylinder was saturated with vapour of carbon tetrachloride and then a methane flame burning at the end of a glass tube was lowered in the cylinder. The flame was extinguished at temperatures above 2O.7 and remained burning at temperatures below 1O.6. At the temperatures between those two the results were doubtful. The vapour pressure of CCI, at Oo is 33 mm. at 8 O . 9 52.5 m.m., thus at about 2O it will have been 40 m.m., consequently, the vapour content of the air must have been about 5

Both phenomena, i. e. the influence on the ignition limit and the extinguishing of the flame, are in harmony with the use of carbon tetrachloride as a fire extinguisher.

V

Experiments with trichlorethylene and technical methane. The boiling point of the trichlorethylene distilled from the commercial product was 87O.2k87O.5.

Burette a. Temperature 5O.O (3.5-3.6 vol. o / o of vapour). No explosion at 7.7, 8.1, 8.5, 8.9, 9.3 and 9 S 0 ' , of methane.

Temperature OO.2 (2.7 vol. of vapour). No explosion at 8.0, 8.3, 8.5, 8.7, 9.0 and 9.6O:, of methane.

These experiments are in accordance with those of Dr. Velisek but prove that the limits of inflammability coincide also when a far smaller quantity of vapour is used.

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Experiments with trichlorethylene and pure methane. The trichlor- ethylene was the same as had been used for former experiments, only it had been kept during two months.

of vapour). No explosion at 5.0 and 5.3: explosion at 5.5, 6.5, 7.8, 8.7, 9.0, 9.3 and 10.2: no explosion at 10.4 and 10.7O/,. The limits are consequently 5.4 and 10.3. of methane.

As carbon tetrachloride had given similar results with .pure as well

Burette c. Temperature 12O.2 (5.3 vol.

596

as with technical methane the above results with trichlorethylene with these two gases were surprising and a presumption existing that the trichlorethylene might have changed during the time that it was kept stored, this liquid was again fractioned.

The experiments with the fraction of boiling point 86O.8-87O.2 now gave the following results :

Burette c. Temperature 14O.5 (5.8 vol. O l 0 of vapour). No explosion at 3.0 and 3.2; explosion at 3.4, 3.5, 4.0, 5.0, 6.0, 7.9, 9.0 and 9.5; no explosion at 9.7 and 9.9. Consequently the limits of inflammability are 3.3 and 9.6 vol. o:o of methane.

Similar results were obtained in burette b. Temperature 14O.5 (5.8 vol. of vapour). No explosion at 2.5; explosion at 2.7, 3.0, 4.0. 9.2 and 9.7; no explosion at 9.9 and 10.4. The limits are 2.6 and 9.8 vol. of methane.

Also similar results were obtained with the vessel of 1 120 C.C. capacity. Temperature 14O.6 (5.8 vol. '/,, of vapour). No explosion at 4.0 and 4.8; explosion at 5.0 and 11.0: no explosion at 11.25 and 11.5. The limits of inflammability are 4.9 and 11.1 vol. Ol0 of methane.

The above proved that in all three cases mentioned a lowering of the lower limit took place. This was in accordance with the results of the experiments formerly made by the first mentioned of us8). A lowering of the lower limit to 2.6 o / o of methane had been observed.

In order to obtain some elucidation of this peculiar phenomenon the first fraction and the last one obtained when distilling the original trichlorethylene were further investigated.

The first fraction was fractioned into three parts boiling at: 70°.5d760.3, 76O.3-85O.O and 85°.0-860.0.

On applying a flame to the first fraction it took fire. At 14O.5 air was saturated with the vapour (about 5.9 vol. This mixture proved to be inflammable (burette b).

The second fraction did not take fire when at ordinary temperature a flame was applied. At 14O.5 (vapour content 5.9 vol. O l i o ) the lower limit of inflammability of methane proved to be lowered to about 1-2 (burette b).

The third fraction gave no explosion at 14O.5 (vapour content 5.8 vol. Ole) with 2.5 o / o of methane; with 2.75 and 3.0 of methane explosion took place.

gave the following results: no explosion at 3.0 O i 0 of methane; explosion at 3.5, 4.0 and 5.1

Most likely a decomposition product originates, when distilling the trichlorethylene, which hastens the further decomposition of the substance.

The last fraction investigated at 14O.6 (vapour content 5.7

of methane.

8 ) Chem. Weekblad 18, 636 (1921).

597

SUMMARY.

The influence exerted by the vapours of carbon tetrachloride and trichlorethylene on the limits of inflammability of a mixture of air and methane has been investigated more closely.

As regards carbon tetrachloride it proved possible to determine the vapour content at which the limits coincide. For trichlorethylene a great difference was found between the results obtained with different preparations, viz.: coincidence of the limits at a low vapour content or the lowering of both limits.

These investigations were made with the financial aid of the “Hoogewerff-Fonds”; we beg to express our best thanks to the Board of Managers.

Le i den, The University, Laboratory for physical and inorganic chemistry.

( R e p le 12 juin 1924).