ELISHA MITCHELL SCIENTIFIC SOCIETY. 57 



It is noticeable that at least four-fifths of the moisture, and in 

 some cases even more, is driven oil" during the first half hour, the 

 remaining one-fifth requiring from 16 to 24 hours additional for 

 complete expulsion. The moisture in the acid phosphates is ex- 

 pelled in a shorter time (16 — 18 hours) than is required for the am- 

 moniates (26 hours), showing that the organic matter in the latter 

 gives up its moisture with considerable reluctance. No definite rule 

 can be laid down as to the amount of moisture expelled in a speci- 

 fied time, as it is entirely dependent on the phosphate itself, the 

 amount of acid used in the preparation, and the condition of the 

 separate particles whether or not they exist in fine state of sub-di- 

 vision. I have observed, however, other things being equal, that for 

 an acid phosphate the smaller the content of Insoluble Phosphoric 

 Acid — indicative of sufficient sulphuric acid in the manufacture — 

 the faster is the moisture expelled and viae versa. 



The method of the Official Agricultural Chemists elsewhere spoken 

 of in this Journal allows 5 hours as the minimum time for the de- 

 termination of moisture in commercial fertilizers. By referring to 

 Table II we notice at the five-hour limit only one sample has ex- 

 ceeded 93 per cent, of the total moisture present, and this one is an 

 exceptional case — the majority being under 90 per cent., one as low 

 as 83 per cent., or a fraction under one fifth of the total moisture 

 present is not estimated if the heating he stop^jed at this point. 



I can only add one word in attestation of the perfect drying prop- 

 erty of concentrated H^SO^ for use in dessicators. Not in a single 

 case with a perfect fitting top did this kind of a dessicator allow the 

 sample to increase in moisture even after it had remained in the 

 dessicator for 93 hours. 



H. B. BATTLE. 



Laboratory of the N. C. Ag. Exp. Station, 

 Raleigh, May 15th, 1886. 



