RAPID GRAVIMETRIC METHOD OF ESTIMATING LIME. 133 



to dryness, and again igniting. The drying of the ammonium 

 carbonate is an especially slow operation, as it has to be 

 clone at an extremely low temperature to avoid spurting. 



If, however, ammonium nitrate is mixed with the calcium 

 oxalate precipitate before ignition, calcium nitrate is formed 

 which is readily and completely converted into oxide on 

 ignition. Five minutes heating over an ordinary bunsen 

 burner is quite sufficient for the purpose. 



The details of the process are as follows : — The calcium 

 oxalate, precipitated, washed and dried in the usual way, 

 is introduced into a platinum crucible together with the 

 incinerated filter-paper. Ammonium nitrate, previously 

 dried at 100° O. and powdered, is added in the proportion of 

 about 0*3 grms to every 0*2 grms of calcium oxalate and 

 mixed as thoroughly as possible with a platinum wire or 

 spatula. Heat must be applied very cautiously as the 

 decomposition is rather violent, and the following precau- 

 tions are to be observed. The crucible is placed in a 

 slanting position and partially covered with the lid, in such 

 a way as to prevent any possible spurting, and at the same 

 time to allow of the contents being under observation. 

 The flame of a bunsen burner is applied to the lid until the 

 mass fuses and solidifies. By this means it is very easy 

 to regulate the heat so that spurting or violent boiling is 

 entirely prevented. The operation, using *1 to *2 grms 

 oxalate and *3 grms ammonium nitrate, takes from 4 to 6 

 minutes. The flame is then placed under the crucible for 

 about 5 minutes longer, the entire operation taking about 

 ten minutes. The whole of the calcium salt is converted 

 into oxide, further ignition over the blowpipe being un- 

 necessary. 



In order to test theaccuracyof the method, determinations 

 were made by the process described, taking pure anhydrous 

 calcium oxalate, with the following results : 



