62 University of California Puhlications la Agricultural Sciences [Vol. 1 



^Moreover, the writer's results are also proof of the fact, as 

 the data in Table I indicate, that even in the absence of salts the 

 reduction method is superior to the colorimetric method where 

 large quantities of nitrates are concerned. 



In the case of soils containing large amounts of organic matter 

 the reduction method is again found superior, since it is fre- 

 quently found impossible to remove the color of a soil extract 

 from such soils without a loss of nitrates. 



So far as my investigations have gone on the subject, and I 

 have tried to take into consideration the several factors involved, 

 no uncontrollable factor has been found to militate against the 

 successful use of the aluminum reduction method. Great accu- 

 racy can be obtained by taking the precautions above described, 

 and reasonable accuracy may be assured in ordinary work with- 

 out the use of such extraordinary measures. The method is 

 strongly commended to the attention of soil investigators in all 

 phases of the work and it is to be hoped that it may serve to 

 render simple and free from annoyance the determination of 

 nitrates in soils under circumstances which until now have pre- 

 sented many difficulties. 



CONCLUSIONS 



1. The aluminum reduction method for the determination of 

 nitrates in soils yields the most accurate results of all methods 

 now commonly in vogue. 



2. "Alkali" salts do not in any way interfere with the success- 

 ful operation of the method. 



3. The presence of extraordinarily large amounts of soluble 

 organic materials (soluble humus and dextrose) have little effect 

 on the method. 



4. A temperature of 20° C. for from 11 to 15 hours has been 

 found the optimum for the reduction of large quantities of 

 nitrates. 



5. The proper amount of NaOH to be employed in the reduc- 

 tion was found to be 2 c.c. of a 50 per cent solution, with an 

 ahiminum strip weighing approximately one gram. 



My thanks are due Prof. C. B. Lipman for helpful sugges- 

 tions and critical reading of the manuscript. 



