394 Chronicles of Science. [July, 



equivalent of hydrochloric acid is added. It is unnecessary to say 

 that the precipitate must he collected and dried with the greatest 

 precaution, since its explosive force is said to surpass that of fulmin- 

 ating mercury. 



While on the subject of explosive compounds we notice Mr. 

 Abel's paper on the " Stability of Gun Cotton," read at the meeting 

 of the Boyal Society on April 4.* One objection brought against 

 the use of gun cotton is its liability to spontaneous changes, some- 

 times resulting in explosion, and in other cases rendering the cotton 

 useless. This, as was stated by Mr. Crookes in an article in our 

 first volume,t is simply the result of imperfect manufacture ; an 

 opinion which the experiments of Mr. Abel confirm. Tri-nitro- 

 cellulose, or perfect gun cotton, is not liable to any spontaneous 

 change; "but the best manufactured article may contain some 

 organic nitrogenized impurities of comparatively unstable pro- 

 perties, which have been formed by the action of nitric acid upon 

 foreign matters retained by the cotton fibre, and which are not com- 

 pletely removed by the process of purification" — that is boiling the 

 raw cotton in a solution of caustic alkali. It is these impurities — 

 not usually amounting to more than two per cent. — which are 

 prone to change when gun cotton is stored in the dry state. 



The first result of the change is the production of a little free 

 acid, and if the change be allowed to proceed it goes on to the com- 

 plete destruction of the cellulose products. But the experiments of 

 Mr. Abel show that the change may be arrested at the primary 

 stage, and the stability of the material ensured for ever. This re- 

 sult is obtained at once by uniformly distributing through the 

 cotton a solution of carbonate of soda. One per cent, of carbonate 

 of soda, Mr. Abel has found, will afford to the material the power 

 of resisting any serious change, even when exposed to such tem- 

 peratures as would cause the decomposition of pure and perfect gun 

 cotton without this protection. 



Water perfectly protects gun cotton from alteration. Actual 

 immersion is not necessary ; if only damp to the touch it undergoes 

 not the slightest change, and may be closely packed in large quan- 

 tities without risk. The safety from explosion Mr. Abel cou- 

 rageously illustrated by taking two or three pounds of damp cotton 

 in his hand, and plunging a red-hot poker into it. Thus gun 

 cotton damped with a proper amount of carbonate of soda solution 

 may be transported without risk to any part of the world, and may 

 then be easily dried for use ; and it is a curious fact that while raw 

 cotton requires a temperature of not less than 240° F. to drive off 

 all moisture, gun-cotton becomes perfectly dry at about 180° F. — 

 the heat required to explode being 300°. 



* 'Proceedings of Eoyal Society,' vol. xv., p. 417. 

 t * Quarterly Journal of Science,' vol. i., p. 407. 



