4 
N. C. AGRICULTURAL EXPERIMENT STATION. 
ton-seed meal was not put through the 40-mesh seive because of its 
low insoluble, and it is not likely that it would be changed by 
such treatment. 
3. Methods .—The idea has long existed in the minds of analytical 
chemists that the nitric and hydrochloric acid methods, either alone, 
modified, or combined, are not safe for getting phosphates in organic 
inaterials into solution in the form to be readily precipitated by the 
ammonium molybdate solution. The trouble has usually been 
credited to the organic matter of the organic materials yielding 
phosphoric acid “playing tricks” with the molybdate solution. 
That these methods are inadequate for total phosphoric acid in cot¬ 
ton-seed meal no one now doubts. The object of the investigation 
was to ascertain if this difficulty extended to other vegetable and 
animal materials containing phosphates commonly used as fertili¬ 
zers and in mixed goods. 
The total phosphoric acid in the results here reported was deter¬ 
mined (1) by dissolving the material in nitric acid and a little 
hydrochloric acid, and (2) by igniting with magnesium nitrate, dis¬ 
solving the residue in hydrochloric acid and a little nitric, and 
following the present official method of the Association of Agricul¬ 
tural Chemists for phosphoric acid. It will be observed that there 
is practically no difference in the results by the two methods with 
any of the materials except cotton-seed meal, which was already 
known to exist. The magnesium nitrate method was not used on 
the bone meal, since numerous experiments here and elsewhere have 
shown the nitric and hydrochloric acid method to be perfectly safe 
for it, where care is taken in getting the solution. 
Soluble phosphoric acid was determined (1) by direct precipitation 
of the water extract of the materials, and (2) by evaporating the 
water extract to dryness, igniting gently, dissolving the yesidue in 
hydrochloric acid and a little nitric, and proceeding as indicated 
above for total. Here, as in the case of total, there is seen to be, on 
an average, very little difference in the results by the two methods, 
save with cotton-seed meal, where the difference is marked and 
important. 
Insoluble phosphoric acid was determined (1) by the regular offi¬ 
cial method of igniting both the “ citrate-insoluble ” residue and 
filter in a small platinum dish, dissolving the ash in hydrochloric 
afcid and a little nitric, and (2) by treating the filter and citrate- 
insoluble residue directly in a 200 c. c. flask with nitric and hydro¬ 
chloric acids. This latter method, though not a recognized official 
one, has been in use in this laboratory for at least four years, during 
which time numerous comparisons of it with the official ignition 
method upon all the fertilizer materials and mixed goods coming 
on our market have been made, and we have vet to find either a 
mixed fertilizer or fertilizer material that will give results materially 
different by the two methods. Cotton-seed meal, which has been 
the source of so much trouble in phosphoric acid work, is not even 
