26 TESTING MISCELLANEOUS SUPPLIES. 



(d) LIME. 



Precipitate with ammonium oxalate from the filtrate from oxid of iron and 

 alumina, filter, wash, ignite, and weigh as calcium oxid or titrate with potas- 

 sium permanganate. 



(e) SOLUBLE SULPHATE. 



Boil 1 giam with 20 cc of strong hydrochloric acid, dilute to 200 cc with hot 

 water, boil, filter, wash, and determine the sulphate in the filtrate by precipi- 

 tation with barium chlorid in the usual manner. Calculate to calcium sul- 

 phate. If carbonates are present calculate the remaining calcium oxid to cal- 

 cium carbonate (whiting) ; if carbonates are absent calculate the remainder 

 as lime. 



(f) Loss ON IGNITION. 



Ignite 1 gram in a platinum crucible. The loss in weight represents water 

 (both free and combined with gypsum and kaolin), carbon dioxid from whiting, 

 and organic matter. 



Barytes should contain only small amounts of foreign matter, and there 

 should be 95 per cent or more of barium sulphate present. 



5. Lithopone. 



Lithopone should contain about 65 per cent of barium sulphate, the remainder 

 being zinc sulphid with small amounts of zinc oxid and carbonate. This sub- 

 stance is also called ponolith and Beckton white. 



(a) ANALYSIS OF PURE LITHOPONE (DEAWE). 

 (1) MOISTURE. 



Heat 2 grams of the sample for two hours at 105 C. There should be less 

 than 0.4 i>er cent of moisture. 



(2) INSOLUBLE AND TOTAL ZINC. 



Take 1 gram in a 200 cc beaker, add 10 cc of strong hydrochloric acid, mix, 

 and add in small portions about a gram of potassium chlorate; then heat on 

 the water bath until about half of the liquid is evaporated. Dilute with hot 

 water. :i<l<l ." cc of dilute sulphuric acid (1:10), boil, allow to settle, filter, 

 wash, ignite, and weigh the insoluble which will be total barium as barium 

 sulphate, together with any other insoluble. Make a qualitative examination 

 for alumina and silica (not likely to be present). Heat the filtrate from the in- 

 soluble to boiling, add sodium carbonate solution, drop by drop, until all of the 

 /iiK is precipitated as carbonate, filter on a gooch, wash, ignite, and weigh as 

 zinc oxid. 



(3) ZINC SULPHID. 



Digest 1 gram with 100 cc of 1 per cent acetic acid at room temperature for 

 one-half hour, then filter and wash ; determine the zinc in the filtrate as in the 

 preceding JUKI lysis. The difference between the total zinc oxid and the zinc 

 oxid soluble in acetic acid multiplied by 1.1973 gives the zinc present as sulphid. 

 The zinc soluble in acetic acid may be reported as oxid, though it may be partly 

 carbonate. This scheme of :m:i lysis assumes the absence of impurities such as 

 salts nf iron, etc.. and is the method of P. I MM we". 



Zts. nngew. Chem., 1902, 16:174. 



