§ 49. CALCIUM. 61 



several times by decantation, and finally rinse it into the 

 filter with hot water. Ignite the precipitate and filter 

 separately (§ 40, J), keeping the filter-ash on the crucible 

 cover. Keep the crucible at a faint red heat 5 or 10 

 minutes at the close of the ignition ; at no time should it 

 be heated to a higher temperature than this ; during this 

 short ignition lift the cover of the crucible a few times. 



After w^eighing, moisten the contents of the crucible 

 w^ith a little water and apply a piece of turmeric-paper 

 to the moist mass ; if the paper is turned brown, rinse it 

 off with a very small quantity of water, put a small 

 lump of ammonic carbonate into the crucible, heat the 

 crucible over the water-bath until its contents are dry 

 again, ignite gently, and weigh again ; repeat this opera- 

 tion with fresh portions of ammonic carbonate, and igni- 

 tion, as long as there is any change in weight. The 

 change of color in the turmeric-paper showed that the 

 first ignition was carried too far, so as to expel some of 

 the carbonic acid, and leave calcic oxide. (Fresenius.) 



The residue of calcic carbonate contains 40 "j^ of calci- 

 um or 56 " Iq of calcic oxide or lime. 



2. If a blast-lamp is at hand, or a gas blow^pipe, it is 

 best to ignite the precipitate of calcic oxalate 10 minutes 

 to an incipient white heat, after the usual ignition to a red 

 heat over the common lamp ; in this way all the calcic 

 carbonate will be converted into calcic oxide, which may 

 be weighed as such ; no testing of the ignited residue is 

 necessary, and moreover the filter may be burned wath 

 the precipitate. 



3. Instead of igniting the precipitate of ammonic oxa- 

 late, after it has been well washed in the usual manner, 

 dissolve it in dilute hydrochloric acid while yet moist, 

 add water in such a quantity that the ratio between the 

 oxalic acid and the water will be about 1 : 400 or 500, 

 a^l to this 6-8 c.c^ of concentrated sulphuric acid, and 

 then estimate the oxalic acid in this solution with the aid 



