278 SOILS. 



charcoal and of calcic carbonate (whiting), the gas was found to consist 

 of pure nitrogen. 



We are forced to conclude that the substances here enumer- 

 ated, as a rule, condense oxygen in smaller proportions than 

 they do nitrogen, or carbonic gas. As regards the carbon 

 monoxid mentioned in the table, it is doubtful that it was con- 

 tained as such in the substance originally examined ; it may 

 readily have been formed under the influence of the heat re- 

 quired in expelling the gases from the substances containing 

 organic matter. Among the important results shown in the 

 table, is the comparative determination of the gases in moist, 

 and in dry garden earth, showing that in the moist earth the 

 amount of gas absorbed ranged from less than one-half down 

 to almost one-fourth that absorbed by the dry. The import- 

 ance of these differences in the case of the fallow can readily 

 be appreciated. 



The changes in the absorptive power brought about by wetting and 

 drying, as shown in the above table, are very insignificant. In the case 

 of the charcoal, soil and silt the diminution may fairly be assumed to 

 be caused by the deposition of soluble salts on the surface, partly clog- 

 ging the pores. In the case of the clay as well as in that of the river 

 silt, the inevitable content of organic matter in process of decompo- 

 sition has doubtless influenced the result, as is suggested by the increase 

 of carbonic gas. That prepared chalk should in one case contain ex- 

 clusively nitrogen gas, in the other case mixed gases, seems to indicate 

 a difference in the air to which it is exposed, or in the water employed 

 in its preparation ; the latter case agreeing substantially with the results 

 obtained from the precipitated carbonate. In both (as well as in the 

 carbonates of barium and strontium), the absorption of carbonic gas is 

 very small, or nil. 



It thus appears that for the condensation of carbonic dioxid 

 gas, ferric and aluminic hydrates are prepotent among mineral 

 substances; while clays, river silts and soils may always be 

 expected to contain relatively large proportions of this gas in 

 absorption. 



