BULLETIN No. 91d. 
5 
an exception to this general rule, which may seem somewhat strange, 
in view of the differences in total and soluble by similar methods on 
the same material. In operating on cotton-seed meal, we have, in 
fact, generally gotten a few hundredths lower by the ignition than 
by the nitric and hydrochloric acids method, due, no doubt, to the 
unavoidable slight loss in incinerating and transferring. All the 
phosphate in cotton-seed meal not immediately precipitable by 
molybdic solution is dissolved by citrate solution. The materials 
operated and reported on here embrace about the complete list of 
raw organic materials yielding phosphoric acid on sale in our State, 
either as mixed goods or alone, and the results, besides giving us a 
better knowledge of their available phosphoric acid and fertilizing 
value, serve to strengthen our confidence in the modification of the 
official method for insoluble. It does not give so nice a solution with 
organic materials as the ignition method, but the saving of time, 
where much work is being carried on, is not inconsiderable 
So far as methods are concerned the following conclusions are 
drawn from the results (table I) on the materials here examined: 
1. That, for total phosphoric acid, the nitric and hydrochloric acids 
and magnesium nitrate methods are equally reliable for all the mate¬ 
rials, except cotton-seed meal, where the magnesium nitrate, incinera¬ 
tion, or sulfuric acid and potassium nitrate method, or some of its 
modifications, must be used.* 
2. That, for insoluble phosphoric acid, direct solution of the 
filter and citrate-insoluble residue in nitric and hydrochloric acids 
and official ignition methods are equally reliable for all the 
materials. 
3. That, for soluble phosphoric acid, the results by the “ igni¬ 
tion ” and “ direct precipitation” methods, compare fairly well in all 
the materials, except cotton-seed meal, where the ignition method is 
the only safe one. 
*See Bulletin No. 8, new series, S. C. Expt. Sta. 
