132 F. B. GUTHRIE AND C. R. BARKER. 



A RAPID GRAVIMETRIC METHOD OP ESTIMATING 



LIME. 



By F. B. Guthrie, f.t.c., f.c.s., and C. R. Barker. 



[Read before ihe Royal Society of N. 8. Wales, September 3, 1902. ~] 



In the determination of lime in analytical work, this sub- 

 stance is almost invariably estimated, after separation from 

 other metals, by precipitation as oxalate from an ammoni- 

 acal or acetic acid solution by means of ammonium oxalate. 

 The precipitate, after thorough washing, is dried and ignited 

 and estimated either as calcium oxide or as calcium car- 

 bonate. Ignition to oxide is the method most commonly 

 adopted. The calcium oxalate precipitate requires strong 

 ignition over the blowpipe for at least twenty minutes, 

 and this must be followed by a further ignition over the 

 blowpipe for 5 or 10 minutes in order to be certain that 

 the weight remains constant. In cases where the pre- 

 cipitate is at all bulky, the complete conversion into oxide 

 is a matter of considerable difficulty and a common practice 

 is to ignite and weigh as carbonate. To do this, the oxalate 

 is ignited at a low red heat. This operation is a very 

 delicate and tedious one, and it is a very difficult matter 

 to avoid converting some of the carbonate into oxide. In 

 the event of this having taken place, the precipitate is 

 moistened with ammonium carbonate solution, dried, and 

 ignited at a heat only sufficient to drive off the excess of 

 ammonium carbonate. Any calcium oxide formed by the 

 first ignition is by this means converted into calcium 

 carbonate. 



This method has the disadvantage that it requires even 

 longer time than the other, and involves three distinct 

 operations; igniting, evaporating the ammonium carbonate 



