228] Analysis of Superphosphate of Lime 141 



if more than 3 grams or less than 1 gram has been taken, then 

 another portion should be taken from the mortar. Two grams 

 should be the quantity used. This is weighed out on a watch 

 glass. The next operation is to mix this thoroughly with water. 

 The method which is most effective is somewhat difficult 

 to describe, though in reality very simple. A beaker about 

 2\ inches high by 1^ inch broad is taken, and the weighed 

 mass of ' super ' is placed in it by means of a stout glass rod 

 3^ inches long. The portion sticking to the watch glass 

 is washed in with not more than 10 c.c. of water. The 

 substance has now to be rubbed round the beaker with 

 the rod very rapidly until it forms with the water a thin paste 

 containing no clots. In doing this the sides of the beaker will 

 become smeared all over with the paste. This is washed to the 

 bottom of the beaker with a jet of cold water, and the liquid 

 made up to about 50 c.c. It is then allowed to stand ten 

 minutes, when it will have settled to a considerable extent. 

 The liquid is decanted through a filter into an 8-oz. beaker. 

 The beaker is filled up again to the same level and decanted off. 

 This is repeated with cold and hot water until all the soluble 

 portion is extracted. The following series of washings should 

 be followed exactly : 



(a) Stir up with cold water 50 c.c. ; 



{b) Fill up twice with cold water 50 c.c. ; 



(c) Twice with hot water 30 c.c. ; 



(d) Boil smartly with 30 c.c. water. 



After the boiling the whole must be transferred to the filter 

 paper and the filtrate tested as it drops from the funnel with 

 blue litmus paper. If an acid reaction is shown, another wash- 

 ing with the hot wash bottle must be given, but as a rule the 

 filtrate is found to be neutral. 



228. Treatment of the Soluble Portion.— This 



