77 S THE POPULAR SCIENCE MONTHLY. 



would dilute the nitric acid, but, as the sulphuric acid has a greater 

 affinity for water, it takes it up, leaving the other of its normal 

 strength. To proceed to the details : Around a brick chimney is placed 

 a wooden trough, containing large earthenware pitchers in which is 

 the acid mixture, the trough being filled with ice. On a shelf above 

 this trough are placed bottles holding glycerine, communicating each 

 with a pitcher below, by means of a small rubber tube, so arranged as 

 to permit the passage of the liquid in a fine stream. The contents 

 of the pitchers are kept in a constant state of agitation by a stream of 

 cold dry air forced through them ; as the reaction between the nitric 

 acid and the glycerine goes on, great heat is evolved, accompanied by 

 nitrous fumes extremely unpleasant and unhealthy to inhale ; these 

 fumes are drawn into the chimney through an overhanging hood, by 

 means of the draught created by a furnace-fire at the bottom. Great 

 care is necessary that the temperature be not allowed to rise above 

 48 Fahr., as there would then be danger of the newly formed nitro- 

 glycerine taking fire and exploding ; constant attention must be paid 

 to this point, each pitcher being tried with a thermometer at short 

 intervals. The proportion of materials is about two pounds of glycer- 

 ine to twenty pounds of the acid, and at the expiration of the process 

 the glycerine and nearly all the nitric acid have disappeared, forming 

 nearly four pounds of their compound ; the sulphuric acid, diluted as 

 before mentioned, also remains. The nitro-glycerine is now partly in 

 solution and partly suspended in the acid mixture ; the contents of the 

 pitchers are poured through a strainer into a vat of water, which is 

 kept in agitation by a stream of compressed air : after all the pitchers 

 are emptied, the air is shut off and the mixture comes to rest, when 

 the nitro-glycerine settles at the bottom of the vat, and the acid water 

 is then drawn off. It is next taken in small quantities at a time, and 

 carefully washed a number of times, until all the acid is washed out, 

 and only the pure nitro-glycerine remains ; in this state it is thin, oily, 

 creamy white, and opaque, but, on being placed in jars and allowed 

 to stand, it soon becomes transparent. It is now ready for use as an 

 explosive agent ; it has a sweet, aromatic, pungent taste, and possesses 

 the very peculiar property of causing an extremely violent headache 

 when placed in a small quantity upon the tongue, or any other portion 

 of the skin, particularly upon the wrist. It has long been employed 

 by homoeopathic practitioners as a remedy in certain kinds of head- 

 aches. In those who work much with it, the tendency to headache is 

 generally overcome, though not always, It freezes at about 40 Fahr., 

 becoming a white, half-crystallized mass, which must be melted by the 

 application of water at a temperature of about 100 Fahr. If perfectly 

 pure that is, if the washing has been so complete as to remove all 

 traces of the acid it can be kept for an indefinite period of time ; 

 and, while many cases of spontaneous decomposition have occurred 

 in impure specimens, there has never been known such an instance, 



