168 WlLKINSON-‘‘HYDROC;EN PNROXIDE IN BLEACmNCt” [&fay 1038

been examined thoroughly in the laboratory. The simple test of dyeing 10 min. without salt at 90” C., showed that the standard RKS brand had a much greater a fb i ty for rayon than the AGS brand, even in the absence of salt, and this explained the uneven results on the large scale.

Salt and sodium sulphate, of course, are not the only salting agents. Not many people know, e.g., that 2% soda ash in a 40:l volume ratio bath salts on Benzopurpurine 4B, although the use of soda ash has been advised fiom time to time for ensuring solubility and penetration. Even the present author recommended its use in his hook on dyeing in 1918, but he is now sadder and more humble since he has tried to use common- sense as the best dyeing assistant. A salting-on agent should not be advised to ensure penetra- tion.

(Patterm illustrating the marked salting effect of soda ash were shown.)

Soap also acts as a sdting agent with salt- sensitive dyes such as Benzopurpurine 4B.

(Dyeings of Benzqurpurine 4B produced insalt- ,free baths with and without 10% soap were shown.)

The fact that soap acts as a salting agent in some cases was first observed by the present author during the dyeing of viscose rayon hanks by the foam method.

The Gerber type of machine is used by the present author for dyeing viscose rayon yarn, and the uneven appearance after the first “strike” is indicated by examination of skeins after making 1, 3, and 5 complete turns in a bath of Sky Blue FF, soap and salt a t 90” C.

(Knitted samples were shown.) A skein makes one complete turn in Q min. on

the machine, so that the distribution of colour after the “strike” in hand dyeing must be more uneven still, when it is remembered that in the case o fa 50 lb. batch, e.g.,the skeins will o d y be turned once in 5 min. If certain dyes, e.g. Chlorazol Fast Orange G, etc., which boil level, are being used, the nature of the f i s t “strike” is of no importance, but if salt-sensitive dyes, e.g. Chlorazol Fast Orange AG, which do not boil level, are being used, the nature of the &st L‘strike” is vital. These points are streased, because it may be thought that the detailed methods of testing a dye as already described are carried too far. In the present author’s opinion, however, these methods are necessary to get the best possible standard of dyeing on viscose rayon with direct cotton dyes, although they are rabed as easy of application.

In view of the large number of dyes used in the average dyehouse, it will be realised what a great amount of patient testing work is re- quired in their examination. It should also be evident that there must be the closest liaison between the dyehouse and the laboratory. The present author’s method is to have every shade matched in the laboratory before it is dyed on the large scale. If a fault develops in the dye- house and cannot be traced, the laboratory staff

try to reproduce it. When this has been donu successfully, the method of prevention on the large scale can usually be found.

HUDDERSFIELD SECTION Joint meeting of the Huddersfield Section and

the Huddersfield Textile Society itt the Technical College, Huddersfield, on 29th January, 1934, Mi. J. F. Copley in the chair.

Hydrogen Peroxide in Bleaching H. W ~ S O N , A.1.C.

(Summary) Hydrogen peroxide was discovered by

Thenard in 1818, and waa first used i n the bleaching of silk about 1878. The present author used it about 36 years ago for bleaching spun silk as follows-The degummed yarn was placed in earthenware pots with R measured quantity of 1 vol. hydrogen peroxide, previously neutralised with ammonia. The pots stood in a tank of water heated to 130” P., the large bulk of water giving a simple means of maintaining a uniform temperature. Bleaching occupied about 12-14 hr. The exhaust liquors were saved, and it was believed at t h e time that these liquors helped to produce a more satisfactory bleaching bath in subsequent operations, a fact which, rightly or wrongly, was attributed tu the presence of a small amount of silk gum in the liquor. The process was easily worked and yielded goods of a uniform whiteness, owing 110 doubt to the rather slow rate of bleaching.

About 1920, improved and concentrated qualities of hydrogen peroxide were manu- factured by the electrolytical process, and in 1925, similar high grade products were rnanu- factured by means of an improved barium peroxide process. The general principles in- volved in these processes are-

New Barium Peroxide Process- (a) H3PO4fBaO2=BaHP0,+ H20, (6 ) BaHPO4+H2S04=H,PO4 tBa804*

Electrolytic Persulphate Process- Electrolysis

(a) 2=so, -+ K,S,O,+H, (6 ) s 0 2~~0Uistlllati011

2 2 *+ .2KHSO,-I H20, The newer 100 and 130 vol. products are

purer, and of greater stabihty than the foriiictr 10 vol. product, whilst the price of the 100 vol. product to-day is one-third what it waa in 1920, so that this fact, together with a greater under- standing of the essential condit,ions of applica- tion, have been sufKcient greatly to increase the importance of hydrogen peroxide as a bleaching agent for many types of material, including all the textile fibres.

Table I gives some particulars of the loss in strength of a number of samples of peroxide

* It;;& be noted that the berium s111plint.c produced iti i~

valuable by-product., N iwt which ynmtly euhi1ct:e the outnitlamid value of this proceea. The liydroyci~ j~eroxlde ia c#n(a:ntrated by distillation.

May 1038J JONES-“STAINS ON HAYON” 160

; i b r prolonged storage. They had been kept hi ordinary soft glass bottles in a laboratory cup- board at room temperature. Samples B and C were qualities not well known in this country; they are included here only for comparison (cf. Table 111).

TABLX 1 ~~

Period of Volume Strength % Acid YRllllllR Storage ~ ~ (w Sulphwic

Acid) Years Dlonths Oriaiual Pitid

( A ) iiiodlcinal (i 2 99.1 ’ 61.5 trace &POI (fi) . . . . . . 4 2 97.6 14.9 064 (a,.. ... 4 2 742 18.3 0.031 (I)) . . . . . 4 2 102.1 62.9 0.11 (H) . . . . . . 4 2 97.1 63.9 0.036 (Y) . . . . . . 1 11 90.8 764 0.032 ( G ) . . . . . . 1 4 1280 115.3 -

_. . - ~~ - .

Weber ( J . Textile Inst., 1933,24,179) has given Borne very interesting data regarding the stab- ility of a large number of samples drawn from their original containers, and they are repro- thioed here along with a test from a 100 vol. sample stored in a paraffined bottle in the dark (cf. Table 11). The inferences to be drawn from these figures are interesting in relation to storage and stability.

TABLP n . ~ ~-

Period of Autliorlty Quality Storage % Average LOSS __ ___

The pH of the bleaching bath hag great i d u - ence on the stability of the bath and the effici- ency of the bleach. Silicate of soda has been widely used for regulating the pH, and appears to have a very useful stabilising effect on the bath. Sodium pyrophosphate ia of more recent introduction and is widely used now, either alone or along with ammonia. In bleaching wool materials by the steeping method, pH 7-2-74, using Phenol Red as indicator, is satisfactory, although in some cases a slightly more alkaline condition, e.g. pH 8, is preferred. The latter gives a quicker bleach, but there may be a loss of oxygen by “gassing”. For bleaching blankets or flannel by the ageing method, it may be best to render the liquor slightly alkaline to phenoI- phthalein, i.e. pH 9-10, because the temperature of the cloth in this case is lower than that of the usual steeping bath, and hence a higher pH may be required to give a sufliciently active bleaching effect. A mixture of sodium pyro- phosphate and sodium oxalate or oxalic acid, known in commerce as Stabilioer C (Laporte), was introduced recently; it is a combined neutralising and stabilising agent for hydrogen peroxide bleaching solutions.

Under normal conditions when bleaching wool, the bath tends to become acid bv the

Weber . . . . ., 12 vol. 1 Year 0-6 oxidation of the immrities, and the im&oved ,. . . . . . . 12 ., 2 ,, 1.4 ... 100 .) 1 ,, 2.0

Wiikinshn ... 100 ,, 1 ,, (special) 0-8

Impurities of any type need to be avoided. The makers take great care to use thoroughly cleansed carboys, which should be kept as cool as possible and away from direct sunlight. When drawing supplies, clean vessels should be used, and care exercised to avoid the entrance of the packing material round the carboy. It is also a good policy to refrain from pouring back into the carboy any excess of the reagent re- moved.

A stability control test used sometimes by the makers is carried out as follows-A suitable quantity of the reagent is placed in a flask fitted via glass connections to a reflux condenser (the apparatus must be carefully cleaned, and several blank tests performed for control pur- poses before using it), and heated on a boiling water-bath, the loss in “vol.” strength being determined at intervals (cf. Table 111). It may be noted thitt products which are not stable to the boiling test, also are unstable on storing as shown by (B) and (C) in Table I.

... 9 7 4

...I 742 ... 97.1

... 101.8 ... 101.1

. . . I 102.0 ,

184 49.1 788 - .- -

After Storage Tat&,

results obtained by ihe use-of this new Geeagent are due to its buffering action.

It is interesting to note that Pehre (Textil- dern . u. Col., 1932, 13, 18), in referring to the use of sodium oxalate in hydrogen peroxide bleaching baths for vegetable fibres, suggests that the substance is absorbed by the fibre, and reacts with the contained hydrogen peroxide to produce an alkaline zone, thus neutralising the acidity produced by oxidation.

MIDLANDS SECTION Joint meeting with the Midland8 Section of

the Textile Institute held a t the Leicester Technical College on 4th Deceinber 2035, Mr. E. M. STEVENSON in the chair.

Discussion on Stains Short summaries of the three contributions

on this subject and of the Hubsequent diuoussioii are given below.

Stains on Rayon T. H. JONES (Summary)

The stains most generally mct with in the processing of rayon fabrics are usually common to all varieties in ordinary use, and may be classified as oil and metal stains, and stains due to floor dirt.

Oil Stains-When these are fresh and ciiusetl by a suitably compounded hutting oil, they are usually fairly easily removed in the norinul scouring operation in presence of suitable alkali,