OF POTASH AND SODA. 163 



burned bones with dilute sulphuric acid, separating the gypsum 

 which forms, and then adding carbonate of potash or carbonate of 

 soda, as long as the liquid has a sour taste, or reddens litmus. 

 The clear solutions thus neutralised are concentrated by eva- 

 poration, and the phosphates separate in crystals when the liquid 

 is set aside to cool. 



If the solution, after being saturated with carbonate of potash, 

 is evaporated to dryness, the first phosphate of potash, contain- 

 ing 43 of acid, is obtained. If it be only concentrated, and then 

 set aside to cool, the second, containing 52 of phosphoric acid, 

 is deposited in crystals. 



All tine three phosphates are permanent in the air, but dissolve 

 readily in w^ater. Only the soda salt is at present met with in 

 the shops, and it is too high in price to be recommended to 

 the farmer. Both, however, might be prepared in a less pure 

 form at a comparatively cheap rate, should experience prove 

 them to be possessed of fertilising properties, which are capable 

 of being made a source of profit to the practical man. 



The equivalent weights of the three salts are 



Phosphate of potash, (a) . . : 207 



.... ... (6) ... 170 



Phosphate of soda, .... 437 



It is only with the first of these phosphates of potash that 

 comparative experiments can be tried against the phosphate of 

 soda. The relative atomic proportions of alkali and acid in the 

 second phosphate of potash are different from those in the phos- 

 phate of soda, and therefore their chemical effects on the soil or 

 on the plant will be different. 



5. Experiments with the phosphates of potash and soda 

 applied alone, and alo'ng with super-phosphate of lime. 



1. The only experiment with the phosphate of soda applied 

 alone which I have met with has been published by Kuhlman. 

 He applied it in 1844 to old grass land, to be cut for hay, in 

 the proportion of 300 kilogrammes of the crystallised salt per 

 hectare dissolved in 1000 litres of water. In 1845 no appli- 

 cation was made, but in 1846 the same substance in the same 



