126 MR. EDWARD SCHUNCK ON SOME 



filtered oflP and washed,, begins gradually to dissolve as 

 soon as the greatest part of the precipitant has been re- 

 moved. I have observed this taking place on washing the 

 precipitate thrown down by acid from the alkaline extract 

 of cotton. When the acid has to some extent been re- 

 moved^ the wash- water begins to become thick and slimy, 

 and runs through very slowly, in consequence of its dis- 

 solving a portion of the parapectic acid of the precipitate. 

 A part also of the pectic acid, originally present, may 

 undergo a further change by the action of the alkali, and 

 be converted into the metapectic acid of Fremy, which is 

 very soluble in water, and is not precipitated by stronger 

 acids. The loss of weight sustained by cotton during its 

 treatment with alkali, and not accounted for by my ex- 

 periments, may therefore be due to such derivatives of 

 pectine as are not precipitated by acid, or are subsequently 

 removed by washing the precipitate with water. 



I have a few remarks to make in conclusion in regard 

 to the part which the bodies naturally accompanying the 

 cellulose of cotton may be supposed to play during the 

 process of manufacturing gun-cotton, and their influence 

 on the quality of the product. In his elaborate memoir 

 on gun-cotton, Mr. Abel attaches some importance to the 

 resinous and other organic impurities of the fibre, and is 

 inclined to attribute the instability occasionally observed in 

 the product to their forming by the action of the acid bodies 

 which are decomposed spontaneously at the ordinary, or 

 a slightly elevated, temperature. It seemed to be, therefore, 

 a matter of some interest to ascertain the nature of the 

 products formed by the action of the mixture of the nitric 

 and sulphuric acids, of the strength employed in the pre- 

 paration of gun-cotton, on the various bodies from cotton 

 which I have described. For this purpose I took, in the 

 first place, a quantity of colouring-matter A, and allowed 

 a mixture of i part nitric acid, of sp. gr. i'52, and 3 parts 



