Mr. F. A. Abel on the Stability of Gun-cotton. 545 



until now ; but since the interesting papers of C. W. Siemens 

 and Professor Wheatstone were read last month, I have carried 

 out the idea as follows : — Two bars of soft iron, measuring 

 7% in. X 2| in. X | in., are each wound, round the centre portions, 

 with about thirty yards of No. 10 copper wire ; and shoes of soft iron 

 are so attached at each end, that when the bars are placed one above 

 the other there will be a space left between the opposite shoes in 

 which a Siemens' s armature can rotate : on each of the armatures is 

 wound about ten yards of No. 14 copper wire cotton-covered. The 

 current generated in one of the armatures is always in connexion with 

 the electro-magnets ; and the current from the second armature, 

 being perfectly free, can be used for any purpose for which it may be 

 required. The machine is altogether rudely constructed, and is only 

 intended to illustrate the principle ; but with this small machine three 

 inches of platinum wire *01 can be made incandescent. 



April 4. — Lieut. -General Sabine, President, in the Chair. 



The following communication was read : — 



" Researches on Gun-cotton. — Second Memoir. On the Stability 

 of Gun-cotton." By F. A. Abel, F.R.S., V.P.C.S. 



The results of the many observations which had been instituted 

 prior to 1860 upon the behaviour of gun-cotton when exposed to 

 diffused or strong daylight, or to heat, although they agree gene- 

 rally with those of the most recent investigations on the subject, as 

 far as relates to the nature of the products obtained at different stages 

 of its decomposition, cannot be regarded as having a direct bearing 

 upon the question of the stability of gun-cotton produced by strictly 

 pursuing the system of manufacture prescribed by Von Lenk, inas- 

 much as it has been shown that the products formerly experimented 

 upon by different chemists varied very considerably in composition. 



The investigations recently published by Pelouze and Maury*, into 

 the composition of gun-cotton, and the influence exerted by light 

 and heat upon its stability, are described as having been conducted 

 with gun-cotton prepared according to Von Lenk's system. The gene- 

 ral conclusion arrived at by those chemists with reference to the latter 

 branch of the subject was to the effect that the material is susceptible 

 of spontaneous decomposition, under conditions which may possibly 

 be fulfilled in its storage and application to technical and warlike 

 purposes ; and the inference is drawn, partly from the results of earlier 

 investigators, and partly from the exceptional behaviour of one or two 

 specimens, that gun-cotton is liable to explode spontaneously at very 

 low temperatures when stored in considerable quantities. 



It has been shown, in the memoir on the Manufacture and Com- 

 position of Gun-cotton, published last yearf, that modifications in 

 the processes of conversion and purification, which appear at first 

 sight of very trifling nature, exert most important influences upon 

 the composition and purity of the product. Gun-cotton of quite ex- 

 ceptional character has been discovered, in several instances, among 

 samples received from Hirtenberg and among the first supplies ob- 



* Comptes Eendus. 



t Trans. Royal Society. [For abstract see Phil. Mag. S. 4. vol. xxxii, p. 145.] 



