352 On Parinr/ and BurniiKf. 



on the calcareous formation of Gloucestershire. In addition to 

 lime, this ash contains a very large proportion of salts of potash, 

 and besides sulphuric acid, soluble silica, and several other less 

 important mineral fertilizing constituents, an amount of phos- 

 phoric acid which is by no means inconsiderable. This acid 

 is evidently united chiefly with lime as phosphate of lime. 



In preparing the ash of couch, it was found extremely difficult to 

 separate adhering clay ; notwithstanding all care the removal of 

 adhering fine soil from the couch was incomplete, as will be seen 

 by a glance at the subjoined analyses. 



Couch on burning furnished an ash, coloured slightly red by 

 oxide of iron, derived no doubt chiefly from adhering clay. 



100 parts of this couch ash were found to contain by my friend 

 and pupil Mr. Kensington, now assistant to Professor Anderson 

 <,'f Glasgow : — • 



Composition of tlie Ash of Couch. 



Potash 10-02 



Soda 5-69 



Chloride of .sodiiun 3-34: 



Lime 5"58 



Magnesia '04: 



Oxides of iron and ahnnina 12"40 



Phosphoric acid 9"38 



Sulphuric acid 5*33 



Soluble sihca 24-92 



Insoluble silicinus matter (chicliy sand) .. IT'SO 



Carbonic acid, and loss 5-80 



100-00 



These constituents probably are united in this couch ash as 

 follows : — 



Carbonate of ])otasli .. .. 14' 10 



Potash in a state of silicate -27 



Soda in a state of sihcate 5-G9 



Chloride of sodium 3-34 



Oxides of iron and alumina 12-40 



united willi i)hosphoric acid 9-38 



equal to bone-earth (20-32) 



Sulphate of lime . . S-OG 



Carbonate of lime 3'30 



Magnesia in a state of silicate '04 



Soluble silica 24-92 



Insoluble silicious matter (sand) .. .. 17*50 



100-00 



The ash of couch it will be observed differs in several respects 

 from that of the stemless thistle. Tlie latter contained but little 

 silica, whilst soluble silica is the chief constituent of couch*. 

 Again, the proportions of lime and potash in the thistle are much 



