136 
IOWA ACADEMY OF SCIENCE 
The precipitation of calcium was performed in accordance with the 
method described by T. W, Richards.*' Oxalic acid was added to the 
hot, acid solution of calcium chloride, the solution was then made just 
alkaline By the slow addition of ammonia, methyl orange being used as 
an indicator, finally excess of ammonium oxalate was added and the 
precipitate was allowed to stand about four hours. 
Ordinary glazed porcelain Gooch crucibles with porcelain plates and 
asbestos mats were used for filtration. Calcium oxalate filters” somewhat 
slowly but the filtrate comes through perfectly clear. The precipitates 
were washed with a dilute solution of ammonium oxalate, finally with 
a little water. 
Calcium oxalate precipitates with either one or three molecules of 
water of crystallization, and gives up this water at 205 degrees centigrade. 
Heating the oxalate for from thirty to forty-five minutes in a drying oven 
at a temperature of 225-250 degrees was found sufficient to dehydrate it 
completely. It behaves very much like the oxide, taking up moisture 
from the air very readily. It is necessary to heat, weigh, reheat for 
ten minutes, dessicate a second time and reweigh rapidly to get the 
correct weight. It is generally possible to get within one or two milli- 
grams of the correct weight at the first trial. ,The results obtained show 
that it is practicable to determine calcium quickly and accurately as 
the oxalate. In heating, I found that the oxalate would not decompose 
though it \vas heated for an hour at 340 degrees. 
As will he seen from the first table (below), the results are well within 
the limits of experimental error. However, to confirm the results obtained 
or to find the error, if any, it was thought wise to weigh also as carbonate, 
if some surer method of converting the oxalate could be devised. De- 
terminations 1 and 2 were heated over a low Bunsen flame without any 
special precautions, dessicated and weighed. In subsequent determina- 
tions, the crucibles were heated high over a moderately large Bunsen 
flame to incipient redness and fairly accurate resutls were obtained. 
A table showing the results of the first series of determinations follows : 
*Ztschr. filer Aiiorg. Chemie, 28-170-(1901) . 
