1839.] 



On Chemical Tests. 



275 



xxiv. Provide a number of test tubes or other glas-es : pour a little of 

 the clear solution into each,* the solution b;ing made somewhat acid, and 

 proceed as follows. Each following letter, from a to u is supposed to 

 be a distinct portion of the solution to be tested, in a different glass, or 

 test tube. 



First. — Examination by means of water*? fully saturated with sulphu- 

 retted Hydrogen. 



xxv. a. Add liquid sulphuretted hydrogen :\ if no precipitate occurs, 

 the base is included from No. 1 to 13. — If a precipitate takes place, the 

 14. Perox: iron. ^ase * s contained in from No. 14, to 25, and 

 16 pJjtox C * d ]Tid m ' ' if tli» precipitatef be white and milky, it 

 n. Ox: bismuth. j s a p roo f that of all the before enumerated 



lis. Deutox : copper. 1 



19. Protox : silver. bases, peroxide of iron, alone, is present ; 



20. Protox : mercury. 1 ' ' * , 



21. Perox •. mercurv. but if it be black, the base is one of those 



22. Ox: gold. * , m . . 



23. Protox : tin. irom 16 to 22. These bases may be thus dis- 



24. Perox : tin. 



25. Protox : antimony. criminated. 



xxvi. b. Add ammonia : if the solution turn blue, the base is deuto- 

 xide of copper : or if the clean blade of a knife, or piece of clean iron 

 be dipped into the solution, it will soon be coated with copper, if cop- 

 per be present. 



xxvii. c. Add a large quantity of water. If a milkiness occurs it in- 

 dicates that the base is oxide of bismuth. || 



xxviii. d.If nitric a; id, and not muriatic acid,has been used, add a drop 

 or two of dilute muriatic acid; a white precipitate will indicate the 

 presence of silver, or mercury. If it be silver, the addition of suffici- 



* In many cases a mere drop of the solution upon a slip of glass may be tested, and 

 the substance be ascertained from the indications given by the test, 

 t Distilled water is always intended whether specified or not. 



X Arsenic is also precipitated by sulphuretted hydrogen, but the metallic oxides are 

 precipitated sooner than arsenic, and may be separated from it by rapid filtration. The 

 filtered solution, (which should smell strongly of sulphuretted hydrogen) may then be 

 boiled and, if a yellow precipitate occurs, which is soluble in hydrosulphuret of ammo- 

 nia, the presence of arsenic may be considered certain. 



\ The word precipitate in its largest signification includes the idea simply of cloudiness 

 or discolouration on the adding of a test. An immediate precipitate depends generally 

 on the quantity, not on the quality, or nature, of a substance. 



I! Other tests in all these, and the following cases may be used, and ought to be, in 

 order to verify the examination. Thus, on referring to the alphabetical list of tests, No. 

 41, bismuth, it will be seen, is discriminated before the blow pipe by fusing into a brit- 

 tle globule that flies to pieces under the hammer ; and if the substance examined is sup- 

 posed to contain several bases, those tests should be selected which are absolutely dis- 

 criminative of only one base if sueh can be found. For instance, clean iron discrimi- 

 nates copper beyond all doubt, and without liability of mistake. See 51 f. and 66. 



