28 TESTING MISCELLANEOUS SUPPLIES. 



Dry 2 grams of the sample for two hours at 105 C. Treat 1 gram in a beaker 

 with 25 cc of water and 10 cc of acetic acid (95 per cent) ; boil, filter, and 

 wash with water. Pass hydrogen sulphid into the hot filtrate, collect the 

 lead sulphid and zinc sulphid on a filter, wash, dissolve in nitric acid, precipi- 

 tate, and weigh the lead as sulphate in the usual manner; calculate to white 

 lead. In the filtrate from the lead sulphate determine the zinc either by the 

 gravimetric or the volumetric method, and calculate to zinc oxid. Test the 

 filtrate from the lead sulphid and the zinc sulphid for barium, calcium, and 

 magnesium, determine in the usual manner, and calculate to carbonates. Trans- 

 fer the residue from the acetic acid digestion to a beaker, add 10 cc of water, 

 10 cc of strong hydrochloric acid, and 5 grams of ammonium chlorid, heat on 

 a steam bath for five minutes, dilute with hot water to 400 cc, boil five minutes, 

 filter, wash, ignite, and weigh the insoluble. Make a qualitative test of the 

 insoluble. Precipitate the lead from the filtrate from the insoluble with hydro- 

 gen sulphid, dissolve in nitric acid, determine as sulphate, and calculate as 

 lead sulphate. In the filtrate from the lead sulphid determine the alumina and 

 the calcium in the usual manner; calculate the calcium found to calcium 

 sulphate. 



BLACK PIGMENTS. 



Black pigments are practically all carbon black in one form or other. They 

 should be tested for oil by washing with ether. Good quality black should 

 be free from oil. Blacks which are alike chemically may behave very differ- 

 ently when ground in thin varnish. For example, lampblack mixed with such 

 varnish in a ratio of 20 : 100 has flow, while gas-black similarly treated has 



DO flow. 



1. Manufactured Blacks, 

 (a) MOISTURE. 



Dry 2 grams for two hours at 105 C. The loss in weight represents the 

 moisture. 



(b) VOLATILE MATTER. 



Heat 1 gram In a well-covered platinum crucible for seven minutes with a 

 Bunsen flame 20 cm high. The crucible should weigh about 25 grams, have a 

 \vcll-titting top, and be supported on a platinum triangle 7 cm above the top of 

 ill" burner. 



(c) ASH. 



Ash 2 grams, preferably in a muffle, and weigh. 



(d) SOLUBLE AND INSOLUBLE ASH. 



A. Id to the ash from 2 grams of black 25 cc of hydrochloric acid (1:1), evapo- 

 rate to dryness on a steam bath, add 5 cc of hydrochloric acid, dilute with 75 

 cc of water, filter through a gooch, wash, ignite, and weigh the insoluble ash. 



(e) ADULTERATIONS. 



Blacks nro ooenaionnlly adulterated with Prussian blue. To determine this 

 point boll the sample with 4 per cent sodium hydroxid, filter, render the 

 tilt ran- Mi-id with hydrochloric acid and add a solution of a mixture of ferrous 

 .UK! f.-rric chlorid or sulphate. A blue precipitate indicates the presence of 

 Prussian Mu>. At least one black on the market contains a large amount of 

 .1 magnetic oxid of iron, which may be readily detected by the action of a 

 nuiKiiet. The ash of ivory and bone blacks should contain a large amount of 

 alcium phosphate. 



