Analyses of Ashes of Plants. 
^77 
soil. To supply the other ingredients in the form of manure of 
mineral composition alone, we must employ an alkaline silicate — 
phosphate of lime and a salt of magnesia. The silicates of potash 
and of soda, as tiiey are manufactured for agricultural purposes, 
are compounds of ver\- varjnng constitution. Of silicate of potash, 
the average amount required for the supply of 84 lbs. of silica 
would probably be about 2 or 2i cwts. It is plain that the quantity 
of potash required by the crop is small when compared with that 
which would be added in the requisite dose of silicate of potash. 
W e would therefore recommend silicate of soda as a more econo- 
mical method of supplying this mineral ingredient of plants. The 
potash must then be applied in another form. 
The total phosphoric acid of the wheat crop would be furnished 
in f cwt. or 1 cwt. of unburnt bones ; the uiagnesia by 40 lbs. of 
sulphate of magnesia (Epsom salts) ; and the potash bv about 
35 lbs. of carbonate (pearlash), or 50 lbs. of nitrate (saltpetre); 
but this last addition will be unnecessary if silicate of potash be 
employed : the necessary top-dressings will then be — 
2^ cwt. silicate of potash, 
1 cwt. of crushed bones, 
40 lbs. sulphate of magnesia. 
Taking into consideration, however, the verv gradual solution 
of the phosphate of lime of bones, it would no doubt be better to 
adopt another form of top-dressing for wheat. The following 
would perhaps be a better application : — 
2 cwt. of silicate of soda, 
1 cwt. of bones dissolved in 
^ cwt. of oil of vitriol, 
40 lbs. of sulphate of maffnesia, and 
35 lbs. of carbonate of potash. 
The bones should be dissolved in the acid previously diluted with 
an equal measure of water : when they become thoroughly broken 
down, the sulphate of magnesia and carbonate of potash shoidd 
be added, and the whole well stirred and left at rest for twenty- 
four hours. At the end of this time the mixture would in all 
probability be found sufficiently dry, when broken up, to be distri- 
buted bv the hand : it might otherwise be mixed with ashes or mould, 
in order to attain the proper condition. 
We have already remarked, that of the total sihca required by 
the wheat, three-fourths belong to the straw, the remainder being 
found in the chaff and grain. On the other hand, by far the largest 
proportion of phosphoric acid is appropriated by the grain. Rea- 
soning upon these facts, we should endeavour, as far as possible, 
to supply the several ingredients at the time when they are 
wanted. 
