ME. ABEL'S EESEAECHES ON GUN-COTTON. 275 



afterwards washed by hand until no longer acid to the taste, and are afterwards placed 

 in crates or perforated boxes and kept immersed in flowing water for about three weeks. 



9. At the expiration of that time the water is separated mechanically from the gun- 

 cotton, and the moist skeins are boiled for fifteen minutes in a solution of potassic 

 carbonate of specific gravity 1"02. When the alkaline liquor has been expressed, the 

 skeins are once more immersed in flowing water for a few days ; the finished gun-cotton 

 is then dried by exposure to air. 



10. It is afterwards allowed to soak for about one hour in a cold solution of sodic 

 silicate of specific gravity 1'072. The liquid is then expressed from the hanks in the 

 usual manner ; after which they are allowed to dry thoroughly, again washed for five or 

 six hours in running water, and finally by hand. The thorough desiccation of the gun- 

 cotton then completes its manufacture. 



The employment of the cotton in the form of hanks of loosely spun yam, instead of 

 simply in the loose carded condition, considerably facilitates its conversion and purifica- 

 tion. The proper impregnation of the cotton by the acids is more rapidly accomplished 

 with the hanks; such manipulations as attend the separation of the main quantity of 

 acid from the converted material, and its first rapid and complete immersion (while still 

 saturated with the concentrated acids) into water, are much more readily carried out 

 with the cotton in the spun form ; and, again, the exposure of the latter- to the full 

 purifying effects of a current of water is much more simply and perfectly effected than 

 if carded cotton be used, while the mechanical loss of wool and of gun-cotton, in the 

 several operations of washing and expressing, is much reduced. I have perfectly satis- 

 fied myself of the advantages just pointed out, by operating upon considerable quan- 

 tities of carded cotton-wool. In these experiments it was found impracticable, more- 

 over, except by application of very powerful pressure, to reduce the proportion of acid 

 which the wool retained after immersion (and which had to be left in contact with it, as 

 prescribed) below that of fourteen parts to one of cotton, whereas with the yam there is 

 no difficulty in reducing the quantity, by moderate pressure, to ten parts, or even lower. 

 The consumption of acid is therefore economized by using the cotton in a spun form. 



The preparation of the mixture of nitric and sulphuric acids, as directed by Von Lenk, 

 involves no important point of novelty ; the necessity of employing the mixture cold, 

 and therefore of either submitting it to refrigeration before use, or preparing a stock 

 of the mixture some time before it was required, was well known to the earlier 

 operators*. 



* An observation made by BficnAjip, in his papers on Pyroxylin, that the production of a soluble or an inso- 

 luble product was determined simply by conditions of temperature, when the conversion was effected by- 

 means of sulphuric acid and saltpetre, induced me to ascertain by experiment whether the solubility, in alcohol 

 and ether, of the product obtained with the employment of the prescribed mixture of nitric and sulphuric acids, 

 increased, if the temperature of the latter was raised to about 70° C. That temperature was fixed upon for 

 the experiment as being the average of the freshly prepared mixture of nitric and sulphuric acids, usually 

 employed for producing gun-cotton for photographic purposes, and which, in experiments instituted, furnished 

 soluble gun-cotton yielding transparent collodion. The products obtained by the action of the warm mixture 



