312 SALTS. 



this gas, together with the nitrogen which is also set at 

 liberty at the same moment, the force of the explosion 

 is due. The sulphur, at the same time, combines with 

 the potassium of the nitre, and remains with it as a 

 sulphuret of potassium. Three equivalents of carbon 

 to one of nitre, and one of sulphur, expresses very 

 nearly the composition of gun-powder. It varies, how- 

 ever, according to the uses for which it is intended, 

 and the country in which it is manufactured. From 

 the proportion, by equivalents, the relative weight of 

 the constituents can readily be calculated. 



788. COLLECTION OF THE GASES. For 



How arc the . -in- / 



gases col- the production and collection of the gases 

 evolved in the combustion of gun-powder, 

 the fuses of ordinary "firecrack- 

 ers" may be employed. Several 

 of them are to be ignited at the 

 same time, in an ordinary test- 

 tube. The mouth of the latter 

 being then brought under a filled 

 and inverted vial, the gases are 

 collected as fast as they are evolved. 



789. NITRATE OF SILVER. Nitrate of 



Describe ni- ., . i j 



trate of silver, silver, or Lunar caustic, is employed, in 

 What are its sur g erVj for cauterizing wounds. A solu- 

 tion of the salt in which the oxide has 

 been precipitated by ammonia, and re-dissolved by a 

 slight excess, is extensively employed as an indelible 

 ink. The black color comes from oxide of silver, and 

 finely divided metal, precipitated in the cloth. It 

 may be removed by soaking in solution of common 



