[ 303 ] 



Besides these compounds of the alkaline earths 

 and alkalies, many others have been recommended 

 for the purposes of increasing vegetation ; such are 

 nitre, or the nitrous acid combined with potassa. Sir 

 Kenelm Digby states, that he made barley grow very 

 luxuriantly by watering it with a very weak solution 

 of nitre ; but he is too speculative a writer to awaken 

 confidence in his results. This substance consists of 

 one proportion of azote, six of oxygene, and one of 

 potassium ; and it is not unlikely that it may furnish 

 azote to form albumen or gluten in those plants that 

 contain them ; but the nitrous salts are too valuable 

 for other purposes to be used as manures. 



Dr. Home states, that sulphate of potassa, which 

 as I just now mentioned, is found in the ashes of some 

 peats, is a useful manure. But Mr. Naismith* ques- 

 tions his results ; and quotes experiments hostile 

 to his opinion, and, as he conceives, unfavourable to 

 the efficacy of any species of saline manure. 



Much of the discordance of the evidence relating 

 to the efficacy of saline substances depends upon the 

 circumstance of their having been used in different 

 proportions, and in general in quantities much too 

 large. 



I made a number of experiments in May and 

 June, 18O7, on the effects of different saline substan- 

 stances on barley and on grass growing in the same 

 garden, the soil of which was a light sand, of which 

 10O parts were composed of 60 parts of silice- 



* Element! of Agriculture, p. 71. 



