loio] soils -PEBTIUZEBS. 317 



it was found that the acidity as measured by the different methods varied 

 with different conditions of moisture and aeration. " With each soil and each 

 method used the samples which had been kept half-saturated wore higher in 

 acidity than they were at the start of the experiment The acidity ot the half- 

 saturated soils was greater than the acidity of the fourth-saturated soils. The 

 soils high iu organic matter showed the greatest acidity when kept fully satu- 

 rated. The soils low in organic matter showed the greatest acidity when kept 

 half-saturated. 



" When the moist samples of soil taken at the close of the experiment were 

 air-dried, the fully saturated samples showed loss of acidity. The half and 

 fourth saturated samples showed both gains and losses in acidity when air- 

 dried. 



"The potassium-nitrate extracts of the fully saturated soils contained much 

 larger amounts of iron than extracts of other samples. This soluble iron 

 was in the ferrous form and was oxidized and made insoluble when the soils 

 were dried. 



'• With the mineral soils the fully saturated soils had much greater amounts 

 of soluble manganese than the other samples. Drying the soils did not render 

 the manganese insoluble as it did the iron. 



"There was less soluble aluminum in the fully saturated mineral soils, but 

 with the soils high in organic matter this was not true. There was both in- 

 crease and decrease of soluble aluminum on drying the soils. 



"Calcium, magnesium, and silica showed variations in solubility owing to 

 different moisture conditions, but the variations were not as striking as those 

 of iron, manganese, and aluminum. 



" In correlating the soluble iron and aluminum with the acidity obtained from 

 the potassium-nitrate extracts, it was apparent that the titrated acidity could 

 not be entirely explained on this basis. Doubtless this acidity is partly due 

 to soluble acid organic compounds. The measurable acidity of acid soils varies 

 to a large degree under different conditions of moisture and aeration. These 

 variations are due to chemical rather than physical changes in the soils. The 

 extreme sensitiveness of the chemical compounds of soils and the wide varia- 

 tions caused by changing moisture conditions leads to the conclusion that some 

 soil investigations should be conducted with undried samples. The soil moisture 

 of acid soils is acid in reaction as shown by hydrogen-ion determinations. 



A list of references to literature cited is given. 



Are unusual precautions necessary in taking soil samples for ordinary 

 bacteriological tests? C. B. Lipman and D. E. Martin (Soil Sri., 6 (1918), No. 

 2, pp. 131-136). — This paper, a contribution from the California Experiment 

 Station, describes tests with bacteriological samples taken from an alluvial 

 loam soil at I lay ward and a blow sand at Oakley, to determine the extent of 

 contamination due to sampling with a post-hole type of auger as compared with 

 sampling with a sterile spatula from the flamed vertical wall of a pit (11. S. R., 

 27, p. 822). Samples were taken for each foot to a depth of 5 ft. and determi- 

 nations made of the number of bacteria which would grow on bouillon agar, 

 the ammonifying power of the soil with 0.1 per cent of peptone, the nitrifying 

 power with soil nitrogen alone and with the addition of 0.2 per cent of am- 

 monium sulphate, and nitrogen fixation in solutions containing 2 per cent of 

 mannite and in soil with 1 per cent of mannite. 



It is concluded that " for ordinary bacteriological work on soils no special 

 precautions are necessary in taking soil samples." No signilicant differences in 

 the points studied were observed between the two methods of sampling. That 

 the sampling itself from the vertical wall constituted a " precautionary " method 

 is said to have been indicated by the marked differences in bacterial manners 



