1917] AGKICULTURAL CHEMISTRY AGROTECHNY. 615 



For the determination of sulphur in soil a 2-gm. charge with 1 gm. of fusion 

 mixture was used. In addition 0.5 gm. of sugar was added and from 10 to 12 

 gm. of sodium peroxid. Some slight precautions were found necessary in the 

 application of the method to sulphur determination in soil. The method as 

 adopted is described in detail. 



The successful use of the bomb method for the determination of phosphoric 

 acid is noted, but because of the easier manipulation of otlier procedures it is 

 not considered desirable. 



The influence of the presence of calcium carbonate on the determination 

 of available phosphoric acid in soils by Dyer's method, Jatindka Nath Sen 

 {Agr. Jour. India, 12 (ISIK), No. 2, pp. 258-265). — Some experimental data on 

 the effect of large amounts of calcium carbonate in soils on the amount of 

 phosphoric acid extracted by treatment with 1 per cent citric acid are sub- 

 mitted and discussed. Other factors which might affect the rate of solution, 

 such as fineness of soil, composition, etc., are also discussed. 



The retarding influence of calcium carbonate was considered not to be 

 solely due to neutralization of citric acid, since the fall in the amount of 

 phosphoric acid extracted was maintained up to a calcium carbonate content 

 of 20 per cent when only 7.1 gm. of calcium carbonate was required to neutralize 

 the citric acid used in the extraction. It thus appears that the phosphoric 

 acid is actually absorbed or " fixed " from the solution by the calcium carbonate. 



Phosphoric acid determination in phosphate rock, C. C Semple (Enffin. 

 and Mill. Jour.. 103 (1917). No. 26, pp. lUO, 11^1).— On account of the difficultj- 

 of obtaining molybdic acid the following procedure was devised for the deter- 

 mination of phosphoric acid in phosphate rock : 



A 0.5-gm. sample of material containing 20 per cent or more phosphoric acid 

 (or a proportionate sample of material containing less) is treated in a 75-cc. 

 casserole with 10 cc. concentrated nitric acid and stirred until all the material 

 is moistened and effervescence ceases. TSventy cc. of concentrated hydrochloric 

 acid is then added and the material gently boiled on the hot plate. If soluble 

 silicates are present they should be dehydrated by evaporating the material to 

 dryness several times with concentrated hydrochloric acid. 



The material is finally taken up with 10 cc. concentrated hydrochloric acid 

 and boiled for a few minutes to dissolve all soluble salts. Boiling water is then 

 added and the material allowed to set until the residue settles, after which the 

 bulk of the solution is decanted on a filter and the filtrate received in a 300-cc. 

 beaker. The residue in the casserole is again treated with concentrated hydro- 

 chloric acid and hot water, and finally transferred to the filter and washed 

 with boiling water until the bulk of the filtrate is about 175 to 200 cc. 



Ammonium hydroxid, a little at a time, is then added to the filtrate until the 

 gelatinous precipitate of calcium, iron, and aluminum phosphates begins to 

 form, after which 30 cc. of ammonium hydroxid (specific gravity 0.9) is added 

 and the liquid well stirred. Ten cc. of a saturated solution of citric acid is 

 added and the solution stirred for two minutes. Enough citric acid should be 

 added to insure complete solution of all the precipitated phosphates. 



Thirty cc. of magnesium mixture is added and the beaker set aside to allow 

 precipitation. It is indicated that, although complete precipitation has been 

 obtained in 1.5 hours, it is advisable to allow at least 3 hours and to keep the 

 filtrate for 24 hours to be certain that complete precipitation has taken place. 

 After complete precipitation the liquid is decanted, the precipitate finally col- 

 lected on a filter, and washed with the usual wash solution, consisting of ammo- 

 nium hydroxid and ammonium nitrate. The filter and precipitate are then 

 placed in a crucible, dried, ignited, and weighed as magnesium pyrophosphate. 



