43, 44] Estimation of Calcium 29 



wash bottle containing dilute HC1 between the clock glass and 

 the edge of the beaker, and blow the acid so that the spray may 

 strike the opposite side of the vessel and descend gently upon the 

 spar. When about 50 c.c. have been added, allow the beaker 

 to stand in a warm place (on the top of the steam oven will be 

 found very convenient) until all effervescence ceases. Should 

 any of the substance remain undissolved, add a little more 

 acid. Remove the clock glass, and wash any liquid adhering 

 to it back into the beaker. 



43. Precipitation. — The precipitate obtained when a 

 solution containing calcium is mixed with one containing an 

 oxalate is of such fine texture that it often passes through a 

 filter paper and thus causes much annoyance. This difficulty 

 may be overcome in the following manner : 



Dilute the solution to about 150 c.c. ; make alkaline with 

 dilute NH 3 , and heat until it just boils. Whilst it is heating 

 weigh out roughly a gram of pure finely powdered ammonium 

 oxalate. Remove the beaker from the flame and add the solid 

 ammonium oxalate a little at a time, stirring continuously. 

 Replace the beaker over the flame and raise to a boil ; then 

 stop heating, and allow the precipitate to settle. This will not 

 take more than a minute or two. 



In using this method care must be taken to remove the 

 beaker from the influence of the flame before adding the 

 oxalate to the solution. If this be not attended to, an effer- 

 vescence will take place which may cause the loss of some of 

 the solution. 



The oxalate should be tested by placing about 2 grams in 

 a weighed platinum crucible and heating to redness. The salt 

 should volatilise entirely, leaving no residue — i.e., the crucible 

 should not gain in weight. 



44. Washing and Filtration.— Wash about six times 

 by decantation, then once or twice on the filter, testing the 



