Penfield and Bradley — Precipitates on Asbestos. 455 



the tube, this may be accomplished by using wire gauze, so 

 placed as to deflect the heat to that portion. 



In order to test the apparatus just described with precipi- 

 tates requiring ignition in gases, a number of experiments 

 have been carried out with the following results : 



Calcium ignited in C0 2 and weighed as CaC0 3 



Precipitated Precipitated 

 as CaC0 3 as CaC 2 04 



Calcite taken 0-7445 0-7191 



CaCO, weighed 0-7450 0-7195 



Error 0-0005+ 0*0004 + 



Error asCaO.... 0-0003 0-0002 



The collection of a considerable portion of calcium oxalate 

 on an asbestos filter can scarcely be recommended because the 

 exceedingly fine precipitate clogs the asbestos and makes the 

 filtration tedious. 



Copper in recrystallized copper sulphate was precipitated by 

 means of hydrogen sulphide and ignited in C0 2 . 



CuS0 4 .5H 2 taken = 0-1936, Cu s S calculated 0-0617 



Cu a S weighed 0*0618 

 Error 0-0001 + 



Zinc in recrystallized potassium double sulphate K 2 S0 4 . 

 ZnS0 4 .6H 2 was precipitated by hydrogen sulphide in formic 

 acid solution ; ignited in C0 2 , and, weighed as ZnS. 



K 2 S0 4 .ZnS0 4 .6H,0 taken 0*5265, ZnO calculated 0*0965 



ZnO determined 0-0960 

 Error 0*0005 — 



Lead in pure galena was precipitated by hydrogen sulphide 

 in acetic acid solution, after decomposing the mineral with 

 nitric acid, and dissolving lead sulphate with ammonium 

 acetate. Lead sulphide was ignited in hydrogen sulphide and 

 weighed. 



Galena taken 0*2494 



PbS weighed 0*2494 



Error . _ 0*0000 



Arsenic in sublimed arsenious oxide was precipitated by 

 hydrogen sulphide after dissolving in pure sodium carbonate, 

 and acidifying with hydrochloric acid. 



The arsenious sulphide was subjected to the action of car- 

 bon bisulphide for the removal of sulphur, using the extractor 

 illustrated by figure 3. 



As 2 3 taken 0*1890, As 2 S 3 calculated 0*2350 



AsjS, weighed 0*2357 



Error 0*0007 + 



