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(5) Soluble Phosphate or Monocalcic Phosphate (CaH 4 P 2 O 8 ); 



(6) Insoluble Phosphate or Tricalcic Phosphate (Ca 3 P 2 O 8 ). 

 1,409. The sample taken should be well ground and 



bluish grey in colour. 



(1) Moisture. Three grams of the sample are weighed 

 out on a watch-glass; and left in the water-oven over-night. 

 Next morning it is covered up and secured with the cover- 

 glass and the clip, put inside the desiccator, and when cool, 

 weighed. It is left in the oven for another hour and treated 

 in the same way ; until the weight is found to be exactly the 

 same as before. The loss of weight is due to the escape of 

 moisture from the 3 grams of the Super. 



(2) Loss on Ignition. One gram of the sample is 

 weighed out in a crucible of known weight, very slowly 

 ignited on low heat, for about a quarter of an hour, until the 

 colour of the whole mass becomes much lighter. It is then 

 laid aside in the desiccator,. and afterwards when quite cool, 

 weighed. The loss of weight is due to the escape of moisture, 

 organic and other readily volatile matter. 



(3) Sand. The residue in the crucible of the one gram 

 just ignited is emptied into a clean beaker, every particle in 

 the crucible being carefully washed out with Hydrochloric 

 acid. A little more HC1 is added, altogether about 50 c. c., 

 and the beaker left uncovered in the sand-bath. When the 

 contents of the beaker become dry, it is taken out, and strong 

 HC1, enough to moisten the contents of the beaker, added. 

 After a quarter of an hour, about 200 c. c. of water are added 

 and the beaker left covered in the sand-bath over-night. The 

 Siliceous residue in the beaker is filtered out on Swedish 

 paper, thoroughly washed, and left over-night in the water- 

 oven to dry. Next morning the Siliceous matter is trans- 

 ferred to the Platinum crucible in the usual way, the paper 

 burnt white, the crucible ignited, left for about half an hour 

 to cool in the desiccator, and finally weighed. The increase 

 of weight of the crucible is due to the Siliceous matter pres- 



