APPENDIX C. 563 



The material remaining on the filter and in the basin, consisting of 

 insoluble earth, carbonates and calcium sulfate, is gently ignited in the 

 basin and weighed ; the difference between this and the first weight 

 gives approximately the total soluble salts, which should substantially 

 correspond to the titrations made. 



The sulfates are determined by differences between these and the 

 total alkalies. The solution may contain some sulfate of magnesia, or 

 calcium and magnesium chlorids, and these are determined gravime- 

 trically. 



Nitrates, which may have been destroyed in the first ignition, are 

 determined in the original solution by the picric method. Any mag- 

 nesia rendered insoluble by the ignition may usually be accounted for 

 as chlorid, unless much nitrate is present which is rarely the case in 

 carbonated alkali. If much nitric acid was found, it should be first 

 assigned to magnesia. 



