MANURES, LIME AND FERTILIZERS 69 
to its popularity. The availability of bone meal depends 
primarily upon its state of division, the finest decom- 
posing most rapidly. 
Sources of phosphoric acid——As previously stated, 
ground bone is used extensively by florists and to some 
extent by vegetable forcers. The phosphoric acid in 
bone meal ranges from 20 to 30 per cent. There are two 
classes, viz., raw bone and steamed bone. Raw bone 
meal is coarser in texture, contains the natural fat and 
decomposes slowly. Steamed bone meal has had the 
fatty material removed by treating the bones with steam 
under high pressure before they are ground. The 
steamed bone meals and flours are of fine texture, and 
for this reason and because of the absence of fats they 
decompose and become available much more quickly 
than the raw bones. 
Acid phosphate may also be used in greenhouse soils. 
In this form, from 14 to 17 per cent of the phosphoric 
acid is available. Floats, or the untreated ground rock, 
might also be used to advantage in greenhouse soils 
which are so heavily charged with organic matter. 
Thomas slag, which contains from 15 to 20 per cent of 
phosphoric acid, should prove satisfactory in vegetable 
forcing. 
Sources of potash.—Of the various forms of potash, 
muriate of potash is used most extensively for open 
ground crops, and there is no evidence that it is not as 
satisfactory as other potash materials for greenhouse 
work. It contains about 50 per cent of actual potash. 
Sulphate of potash, another product of the German 
mines, contains about the same percentage of potash as 
does muriate of potash, though the purer grades carry 
larger amounts. ‘Tobacco stems and wood ashes are 
also available as sources of potash. 
