1871-] War Science. 51 



The method of testing this particular quality in gunpowder 

 is at once so simple and interesting that we do not hesitate 

 to describe it here in detail ; an instrument, termed a densi- 

 meter, is used for the purpose, consisting of an oval glass 

 bulb, of which the upper end is in connection with an air- 

 pump, while the lower one terminates in a tube dipping into 

 a bowl of mercury. Into this glass globe, which is furnished, 

 we should mention, both at the top and bottom, with stop- 

 cocks, is placed a certain quantity, say 1000 grains, of gun- 

 powder, which •fills up, perhaps, one-half or two-thirds of 

 the available space ; the vessel is screwed into connection 

 with the air-pump, and the lower stop-cock having been 

 closed, the air is exhausted from the interior of the bulb. 

 When this has been effected, the upper stop-cock is closed 

 and the lower one opened, upon which the mercury from the 

 reservoir placed underneath rushes into the tube and com- 

 pletely fills up the vacuum, so that nothing is actually con- 

 tained in the glass vessel but powder and quicksilver. In 

 this condition the bulb is disconnected from the air-pump 

 and accurately weighed, and the heavier the result, or, in 

 other words, the more mercury there is present, the denser 

 must be the powder, for the latter, if of a compact nature, 

 takes up but little room and leaves a larger space for the 

 mercury ; if, however, the gunpowder under examination 

 happens to be of a light, porous description, the 1000 

 grains of material will of itself have filled up the greater 

 part of the bulb, and the quicksilver in that case has 

 found but limited space therein. Of course, when the weight 

 of a standard powder has been fixed upon, it is a very easy 

 matter to institute a comparison between it and the product 

 under examination, and an accurate result is thus readily 

 obtained. This, then, in a few words, is the method adopted 

 for examining all supplies of powder made in the Government 

 Mills, at Waltham Abbey, or sent in by contractors, for the 

 War Department factory is, by itself, incapable of turning 

 out the large quantity of gunpowder expended annually by 

 our army and navy, even in times of peace. 



Passing to other questions referred to the Chemical Depart- 

 ment, perhaps the most interesting are those affecting the 

 supply of stores to the army. It forms, in fact, one of the 

 principal duties of the Government chemists to examine 

 rigorously into the nature of all military necessaries, and 

 upon the chemical report alone depends, in great measure, if 

 not altogether, the acceptation, or rejection, of supplies. 

 Thus, contracts for such articles as soap, candles, bees'-wax, 

 oils, paints, tallow, and other necessaries too numerous to 



