236 ALKALIES. 



&c. ; acids bring the colors back, as has been stated in giving the 

 general characters. 



(b.) In applying these colors, we may fill a small tube stopped at 

 one end, or an essence vial, with the colored fluid, and with a finger 

 on the mouth, turn it upward into a jar of the gas standing over mer- 

 cury ; instantly the color will change, and the gas be absorbed. 



9. CONDENSATION OF THE GAS, BY COLD AND PRESSURE. 



This was accomplished by Mr. Faraday,* by disengaging it in 

 sealed syphon tubes, from chloride f of silver which absorbs it in 

 large quantities, 100 grains absorbing 130 cubic inches of the 

 gas. The leg of the syphon containing the chloride, was heated to 

 100 Fahr. and the other leg kept cold by ice. Ammoniacal gas was 

 evolved, and part of it was by the pressure of the rest, reduced to the 

 liquid state. It was a colorless fluid ; its refractive power was great- 

 er than that of water, and at 50, its pressure equalled 6.5 atmos- 

 pheres ; its specific gravity was 0.76, water being 1. 



10. PROCESS IN THE ARTS. 



By the distillation of bones, and other firm parts of animal sub- 

 stances, ammonia is generated, by the reaction of its elements, but 

 it is more or less combined with carbonic acid. Among the ele- 

 ments of animal matter, we always find hydrogen and nitrogen. The 

 ammonia obtained is impure, mixed with animal oil, &c. and is pu- 

 rified by combining it with the muriatic or sulphuric acid, and then 

 decomposing this ammoniacal salt by quick lime, in the manner alrea- 

 dy described. In the manufactories, bones and horns are commonly 

 employed, and sometimes the refuse of the slaughter houses. An 

 iron retort, or still is generally used ; the bones are introduced rough- 

 ly broken, and a strong heat applied. A tar like substance, oil, and 

 very fetid gases, are evoked, which should always be burned as 

 they are both noxious and disgusting. Valves are sometimes fixed 

 in the apparatus to prevent the return of common air ; this would of 

 course happen when the apparatus grows cold, and the air by ming- 

 ling with the inflammable gases, might occasion an explosion, when 

 the fire is lighted again. Animal charcoal, mixed with phosphate of 

 lime, remains in the iron vessel. J 



11. PHARMACEUTICAL PROCESS. 



To procure aqua ammoniae, we may employ either a still or 

 Woulfe's bottles ; the latter are always used in philosophical laborato- 

 ries ; the proportions of the materials are 1 to 2 parts of slacked lime, 

 and 1 of pulverized sal ammoniac, and the gas is received in water, 



* Phil. Trans. 1823, p. 196. I Muriate. t Gray's Op. Chem. 



In the large way, one ofiron is used with a stone-ware head, and stone- ware bot- 

 tles may be used for the condensation. 



