S12 



On Chemical Tests. 



[Oct. 



remaining solution containing the nickel, after being heated to expel 

 the sulphuretted hydrogen was decomposed by caustic soda; this gave 

 hydrate of nickel, which, -when reduced to protoxide by strong ignition, 

 weighed 20.1 grains. In this experiment there was a loss of 0.2 grains 

 of copper, and a surplus of 0.1 grain of oxide of nickel ; errors so small 

 that they are evidently those of manipulation. London and Edinburgh 

 Journal, vol. 8, page 81, 1836. 



c. — N Urate of copper is reduced by zinc, lead, cadmium, and tin: 

 cobalt acts very slowty, and bi.->muth but imperfectly even when the 

 solution is hot. The reduced copper appears with metallic lustre only 

 upon cobalt, lead, and clean iron, with other metals it forms a brown, 

 or black alloy. Chloride or muriate of copper is easily decomposed by 

 iron, tin, zinc, cadmium, and cobalt, and slowly by lead if the solu- 

 tion be not acid. The ammoniacal solution of copper is reduced only 

 by zinc, iron, and cadmium, not'by tin, lead, or cobalt. Zinc is by far 

 the most effectual precipitant of copper. 



53. CORBOSSVE SUBLIMATE called also per -muriate ; oxymurU 

 ate ; bichloride, and perchloride of mercury detects albumen and ammonia ; 

 heat must be employed to separate the whole of t]ie albumen contained 

 in any solution ; it will fall down in a flocky precipitate, which when 

 carefully dried will contain about 78 per cent, ol albumen. To de- 

 tect ammonia, see 28. Corrosive sublimate is detected by lime water, 

 see 75.85. 



a. The perchloride of mercury in solution removes stains on the 

 skin caused by nitrate of silver, and it also effaces the so called 

 indelible ink for marking linen, the base of which is nitrate of silver, 

 or the lunar caustic of the apothecary. 



54. FLUORINE fiuates, fluoric acid, these substances are detected 



by glass, thus ; the fluoride, or fluate is to he reduced to powder, and 

 mixed with sulphuric acid to the thickness of paste, it may then he put 

 into a leaden dish, and heated over a spirit lamp ; fluoric acid will 

 escape, and if glass he held over its fumes it will he thereby corroded. 

 If the glass is covered with w ax and tracings be marked on it down 

 to the glass, etchings may be produced. The gas, or fumes of the 

 acid are poisonous, and must not be inhaled. See 18, a. 



55. GALLS, tincture of, detects iron in solution turning it black or 

 purple. See 8. 65. Alkaline or earthy salts, if present, influence 

 the colour changing it to violet or purple. Sulphate of lime 



