72 Preparation of Substances 



making 12CaO used for every lOCu; or 

 more in detail, 9Ca02H2 were necessary to 

 react with 9CuS04 before the resulting 

 9CUO2H2 could form 9CuO and 3CaO are 

 found in the product making a total of 12CaO 

 required. The lOCu come from 10CuSO4- 

 5H2O and thus the ratio between copper 

 sulfate and lime, 10CuSO4-5H2O/12CaO, is 

 estabUsht. In figures it is 2497.3/672 or 

 3.7 showing that nearly four times as much 

 Hme is used as is cald for by the symbol. 

 This ratio has been fixt by horticultural 

 practise. 



From the previous paragraf it is evident 

 that nearly four times as much hme is used 

 as is needed. The student will inquire as to 

 what becomes of the remainder. The solu- 

 bnity of calcium hydroxid at 25° is 0.16 

 gram in 100 cc. of water. This amount, 

 however, is lessend by the presence of cal- 

 cium sulfate so that only a small portion of 

 the whole amount of lime dissolvs in water. 

 Further, not all the lime weighd out gets 

 into the preparation, as lumps, air-slaked 

 material and frequently lime itself may be 

 rejected by the strainer. It is obvious that 

 all the lime not in solution must be mixt in 

 with the precipitate. 



The white scum is calcium carbonate 

 made up of carbon dioxid from the air and 



