190 F1LMINATING MERCURY. 



the wire, as a preliminary experiment (with Mr. Cuthberf 

 electrometer) had .shewn me would, by making the wire red hot, 

 inllamc the powder. The glass globe withstood the explosion, and 

 of course retained whatever gasses were generated ; its interior 

 was thinly coated with quicksilver, in a very divided state. A 

 bent gla>s tube was now screwed to the stop. cock of the brass cap, 

 which being introduced under a glass jar standing in the mercurial 

 bath, the stop-cock was opened. Three cubical inches of air 

 rushed out, and a fourth was set at liberty when the apparatus was 

 removed to the water tub. The explosion being repeated, and the 

 air all received over water, the quantity did not vary. To avoid 

 an error from change of temperature, the glass globe was, bofh be- 

 fore and after the explosion, immersed in water of the same tem- 

 perature. It appears, therefore, that the ten grains of powder 

 produced four cubical inches only of air. 



*' To continue the comparison between the mercurial powder 

 and gunpowder, ten grains of the best Dartford gunpowder were 

 in a similar manner set (ire to in the glass globe : it remained en. 

 tire. The whole of the powder did not explode, for some com. 

 plete grains were to be observed adhering to the interior surface of 

 the glass. Little need be said of the nature of the gasses generated 

 during the combustion of the gunpowder : they must have been 

 carbonic acid gass, sulphureous acid gass, nitrogen gass, and (ac- 

 cording to Lavoisier) perhaps hydrogen gass. As to the quantity 

 of these, it is obvious that it could not be ascertained : because the 

 two first were, at least in part, speedily absorbed by the alkali of 

 the nitre, left pure after the decomposition of its nitric acid." 



The following description will give the experimental philosopher 

 a clear idea of the instrument used in this business. 



The ball or globe of glass is nearly half an inch thick, and seven 

 inches in diameter. It has two necks, on which is cemented two 

 brass caps, each being perforated with a female screw, to receive 

 the male ones; through the former a small hole is drilled; the 

 latter is furnished with a perforated stud or shank. By means of 

 a leather collar the neck can be air-tightly closed. When a por- 

 tion of the powder is to be exploded, it must be placed on a piece 

 of paper, and a small wire laid across the paper, through the midst 

 of the powder ; the paper being then closed, is to be tied at each 

 end to the wire with a silken thread. One end of this wire is to be 

 fastened to the end of the shank, and the screw inserted to half its 

 length into the brass cap ; the other end of the wire, by means of a 



