1839.] 



On Chemical Tests. 



337 



dissolving silver directly in nitric acid, the silver should be pure. Pure 

 silver may be obtained by mixing carbonate of potash with precipitated 

 muriate of silver, and melting the mixture in a strong heat. The re- 

 sult will be pure metallic silver. The muriate of silver before it is melt- 

 ed should be well washed with pure water. 



109. silver, sulphate of, is used sometimes in analysis in prefer- 

 ence to the acetate, or nitrate, but similar precautions should be 

 adopted, as in using the nitrate of silver. 



HO. SODA and its salts, may be distinguished from potash and its 

 salts by tartaric acid, and chloride of platinum, see 19, and 98. Salts of 

 soda tinge the outer flame of the blow-pipe yellow, which is the best 

 discriminative test. 



a. Potash and soda may be very readify distinguished by the micros- 

 cope thus. Add nitric acid and thus change the alkali into nitrate of 

 soda, or nitrate of potash as the case may be. Spread a drop on a slip 

 of clean glass and slowly evaporate it; place the glass under the mi- 

 croscope and if the base be soda, cubic or rhomboidal crystals will be 

 seen, but if potash, needle-like crystals of saltpetre ; the solution 

 should not be too concentrated, nor the evaporation too rapid, or the 

 crystals may become confused and irregular. 



b. The solutions of the neutral phosphate, arsenite, borate, and car- 

 bonate of soda, and of fluoride and sulphuret of sodium, turn reddened 

 litmus paper blue. 



c. Carbonate of soda, used as a test, may be examined in the same 

 manner as carbonate of potash, see 98 d. 



111. SODA, succinate of, see 36. 



112. SODA, sulphate of, or sulphate of potash detects lead. The 

 precipitate, sulphate of lead, is insoluble in water and in liquid am- 

 monia, but soluble in dilute nitric acid, when assisted with heat. The 

 solution is blackened by sulphuretted hydrogen gas. These indications 

 distinguish sulphate of lead from sulphate of barytes. 



a. Sulphate of soda as a test should not contain an excess either of 

 acid, or of alkali ; both of which may be ascertained by blue, or redden- 

 ed litmus; see 77, 78, nor should it contain earthy or metallic salts; 

 the former of which are detected by carbonate of potash, and the latter 

 by prussiate of potash. If it contains muriate of soda, it may be detect- 

 ed by sulphate of silver. 



