312 BULLETIN OF THE BUSSEY INSTITUTION. 
The results with sand, and those with coal ashes * also, go to 
show that the process would be applicable for testing some kinds 
of coarsely powdered rocks, such as granite * for example, but 
with single minerals the case is different. For testing a mineral 
(phosphate rock for example,) it is not sufficient to mix it with an 
inert sand, since the mechanical texture of the sand is apt to be 
very different from that of the powdered mineral§ and since the 
sand may not contain enough of the subordinate kinds of plant- 
food to meet the requirements of the case. The results recorded 
in the lower table on page 000, show indeed that the plants got 
some phosphoric acid from the phosphate-rock, the bone-black, 
and the green sand of the experiments, but it was plain that the 
crops did not derive nearly so much benefit from these materials as 
they might have done under more favorable conditions. Instead 
of inert sand there is needed a more generous material, such for 
example as a calcined loam of known value which should contain 
all the inorganic elements of plant-food. But since experience 
teaches that it is not easy to distinguish one such loam from 
another, there is little reason for hoping that the value of the 
phosphate-rock would be properly exhibited in case it were ad- 
mixed with the loam. Instead of pursuing this line of inquiry, I 
. sought rather to find a sand which would meet the requirements of 
the case, and in view of the importance of having some organic 
matter in the soil, to help dissolve the phosphate or other mineral, 
I incorporated the powder to be tested with a mixture of inert 
sand and peat that had been thoroughly leached first with hot mu- 
riatic acid and then with rain-water until the acid had all been 
removed. But the experiments made in this way, with phosphate- 
rock, mica-clippings, bone-black, and bog-iron ore, were not satis- 
factory. The soils thus constituted were cold and sour and soggy ; 
the buckwheat plants that stood in them were sickly and dis- 
tressed, and it was plain that no just conclusions could be drawn 
from results obtained under such conditions. Possibly, the free 
humic acid which must have resulted from the action of the muri- 
atic acid in removing bases from the peat, was hurtful to the 
plants? If I were to repeat the trials, I would seek for a natural 
peat that contained very small proportions of nitrogen and ash in- 
gredients, and would employ it admixed with sand as the normal 
earth in which to test a powdered mineral. 
* Bussey Bulletin, 1. 50; 2. 159. 
