_Discussion of the Table._—It will be observed that in this table, the largest amount of total gas given off by equal weights of any one substance was in the case of carbonate of magnesia; but it is quite probable that in part, at least, this large amount of gas was due to the evolution of carbonic gas from the easily decomposable carbonate; the more as the analysis of the gases shows over 29% of carbonic gas. But the highest absorption by equal _volumes_ of any substance is shown by the ferric hydrate; next to this by the light poplar charcoal, and next by the carbonate of magnesia. The high absorptive power here shown by the ferric hydrate is of great interest in connection with the facts already stated regarding the absorption of moisture and ammonia by ferruginous soils (see page 274, this chapter); and the fact that the larger proportion of the gas—as much as 70% in one case—consisted of carbonic gas, is particularly interesting in the same connection. Both in the amount of gas contained, and in the proportion of carbonic gas therein, the ferric hydrate exceeds even peat, the representative of humus in soils. It will, however, be noted that in the garden soil, also, the proportion of carbonic gas is very large, while that of oxygen is very low. It is curious to note that in very few cases the proportion of oxygen to nitrogen is the same as in the atmosphere; in most cases the nitrogen predominates considerably beyond its normal proportion, and in two cases, that of charcoal and of calcic carbonate (whiting), the gas was found to consist of pure nitrogen. We are forced to conclude that the substances here enumerated, 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 contained as such in the substance originally examined; it may readily have been formed under the influence of the heat required 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 importance of these differences in the case of the fallow can readily be appreciated.