86 DR HAY ON THE CHEMISTRY OF NITROGLYCERINE. 



being heated over the water-bath. I have heated pure nitroglycerine to the 

 highest possible temperature over the water-bath for four hours, and have 

 never observed the development of the slightest colour or decomposition. 

 When it decomposes under such circumstances it probably contains free acid 

 or alkali. Again, it is stated by Railton* that when placed in the bell-jar of 

 the air-pump it rapidly undergoes decomposition. In the course of the investi- 

 gation by Mr Masson and myself, we have kept nitroglycerine for twelve days 

 in vacuo without its exhibiting the slightest signs of decomposition. The 

 decomposition of Railton's preparation must have been due to its impurity. 



Nitroglycerine has no odour when cold, but emits a pungent odour when 

 heated. Although odourless in the cold, it nevertheless seems to be under- 

 going slight volatilisation ; for after working with it for a short time, and. without 

 directly touching it with the fingers, I have generally experienced its physio- 

 logical effect in a slight degree. Its taste is sweet, and not unlike that of 

 glycerine, but is more pungent. 



As regards its solubility, 1 gram, dissolves in about 800 c.c. of water ; 

 with difficulty in 3 c.c. of absolute alcohol, easily in 4 c.c. ; in 105 c.c. of 

 rectified spirit (sp. gr. - 846) ; in 1 c.c. of methylic alcohol (sp. gr. , 814) ; in 

 4 c.c. of methylated spirit (sp. gr. 0"830) ; in 18 c.c. of amylic alcohol; in every 

 proportion in ether ; so also in chloroform, in glacial acetic acid, and in carbolic 

 acid; in less than 1 c.c. of benzol; in 120 c.c. of carbon bisulphide; and to a 

 very limited extent, if at all, in glycerine. 



Method of Estimating Nitroglycerine. — In cases where nitroglycerine 

 cannot be estimated gravimetrically after extraction with one of its solvents, 

 a method based on the evident constancy of the amount of the nitrous acid 

 produced in its decomposition with potash may be safely adopted. I have 

 made use of this method for ascertaining the degree of its solubility in water, 

 and for other quantitative estimations in the course of this investigation, 

 and it is not difficult to apply. The materials necessary are a standard 

 solution of pure nitrite of sodium (titrated with permanganate) of the 

 strength of 1 in 1,000,000, a well-boiled solution of starch and iodide of 

 potassium, dilute sulphuric acid, and pure potash, ascertained to be free from 

 nitrous acid. Heat the fluid containing the nitroglycerine with excess of 

 potash, and dilute with water until, in comparison with the standard solution of 

 nitrite of sodium, it yields a blue colour with the starch mixture and sulphuric 

 acid of precisely the same depth. From the degree of dilution required the 

 amount of nitrous anhydride present can be readily calculated, and this amount 



multiplied by 33 .^ g (33-48 being the percentage of nitrous anhydride yielded by 



nitroglycerine) will give the quantity of nitroglycerine. 



* Op. cit. 



