322 



CHEMICAL MANUEES. 



Common salt and soluble sulphates may be eliminated by washing 

 with cold water and by centrifuging. The content in nitrate is 

 evidently not always constant ; it generally varies between 90 and 

 100 per cent, which corresponds to a strength in anhydrous nitric 

 acid of 57-2 t3 63'5 or of 14-8 to la-4 per cent of nitrogen. In 

 Great Britain the fraction which goes to make up 100 per cent is 

 regarded as refraction, so that a nitrate of 5° of refraction means a 

 •nitrate of 95 per cent strength. This remark is important, so as to 

 understand market reports. On different occasions chlorate and 

 perchlorate of potash have been found in nitrates. Now these sub- 

 stmces are liable to spontaneous combustion, besides they are 

 injurious to vegetation. The presence of perchlorate is attributed 

 to the negligence of the workmen who have omitted to cool the 

 solution of caliche in the pan and have set it aside to crystallize in 

 the hot state. This perchlorate may be extracted from the substance 

 by the method which was the subject of German patent No. 125,206. 

 But since the disastrous effect of perchlorate on vegetation has been 

 recognized and the nitrates which contain it refused, manufacturers 

 have been more careful, and perchlorate is now only rarely met with 



in nitrate. 



One hundred parts of water dissolve of nitrate of soda at 

 ■0° 10° 20' 30° 40° 100° 121° Boiling-point of the solution. 

 .71 78 88 98 109 178 224-8 Parts. 



The specific gravity of nitrate of soda is 2-244. 



Nitrate of Potash. — A compound of nitric acid vfith potash has 

 •no interest but for industry ; it is too dear to be used in agriculture, for 

 up to now it is only made from Chili saltpetre and potassium chloride. 

 It forms in itself an excellent manure, seeing that it contains not 

 ■only nitrogen but also potash in a very pure form. Lately, however, 

 important deposits of nitrate of potash have been discovered in South 

 Africa, especially in the neighbourhood of Mabelstadt, and of Peliska 

 in Cape Colony. But these deposits do not appear to be exploited. 



Before terminating this subject, mention may be made of a 

 nitrogenous manure put on the market in 1874, which has given 

 good results. It is a double nitrate of potash and soda ; it contains 

 in 100 parts, according to Maercker : — 



TABLE LXVIL— ANALYSIS OF A DOUBLE NITRATE OF POTASH 



AND SODA. 



