Apr. IS. I9I5 Availability of the Nitrogen in Kelps 23 



lizing material present, this figure being determined for each set on 

 other dupHcate portions. The whole solution was thoroughly mixed 

 and an aliquot portion taken for the determination of nitrates by the 

 aluminum-reduction method. The essential procedure as outlined by 

 the American Public Health Association (i, p. 25) was followed. Pre- 

 vious work with this method on sewage samples, which were solutions 

 of essentially the same type, had shown it to be very satisfactory for 

 nitrate determinations. Burgess (6) has also found this method excel- 

 lently adapted to the determination of nitrates in soils. The accuracy 

 of the above procedure was also checked by running several series of 

 triplicate determinations in which 200 gm. of soil were taken and dis- 

 tilled with magnesium oxid, as shown above, and the nitrates in the 

 residue determined. To other triplicate sets varying quantities of potas- 

 sium nitrate were added. They were then similarly analyzed. The 

 agreement throughout was excellent. In some cases it was absolute. 

 In none did the divergence exceed the ordinary analytical variation. 



SERIES I.— COMPARATIVE AMMONIFICATION AND NITRIFICATION OF 

 DRIED KELP, DRIED BLOOD, AND COTTONSEED MEAL, USING CLAY 

 ADOBE SOIL 



In the first series Macrocystis pyrijera, Nereocystis luetkeana, and 

 Pelagophycus porra were each used in the proportion of 10 gm. of dried 

 and ground kelp to 200 gm. of fresh field soil. This soil was taken from 

 the campus botanical gardens and was in texture a slightly modified 

 clay adobe. In order to compare the kelp with substances of well-known 

 availability, portions of i gm. of dried blood and 2 gm. of cottonseed 

 meal were also added to duplicate sets of tumblers, while blank deter- 

 minations of untreated soil were started to determine the ammonia and 

 nitrate production occurring in the natural soil. The kelp employed was 

 in each case a composite made up from the analytical samples of that 

 variety. These had been dried to a constant weight at 100° to 105° C. 

 for a period of three to nine hours and then ground so as to pass through 

 a 0.5-mm. sieve. The percentage composition of the kelp was as follows: 



Total soluble 

 Species of kelp. Moisture. Nitrogen. salts. • 



Macrocystis pyrijera 4- 71 i. 07 30. 77 



Nereocystis luetkeana 5-24 i. 66 46. 83 



Pelagophycus porra 4-36 i. 22 45-64 



It will be noted that the moisture content was fairly uniform in all 

 varieties, while both the A^. luetkeana and P. porra, as usual, contained 

 larger quantities of nitrogen and total soluble salts than the M. pyrijera. 

 The composition of the salts, both soluble and insoluble, added to the 

 soil when applying kelp will be of considerable interest in this connection. 

 It was impossible to make complete ash analyses of all the kelps used 

 throughout these studies. Mr. P. L. Hibbard, of this laboratory, how- 

 ever, has made analyses of representative plants of each species, and it is 



