252 CALX INCREASING THE SUPPLY OF CARBON. 



their constitution as to dispose them to reflect, under the ordinary 

 defects of climate and season, their natural green ; and, by con- 

 necting this power with the other and well-known events in the 

 series, viz. the more active decomposition of carbonic acid, where- 

 by more carbon, the basis of vegetable matter, is assimilated, and 

 more oxygen returned to the atmosphere, we obtain, as is conceived, 

 a consistent explanation of the action of lime, both in the pro- 

 motion of the fertility of the soil, and in the restoration of the 

 air to its purity." Observations, &c., pp. 9, 10. 



These interesting experiments have still later been repeated by 

 Dr. Wight, and always with the like results. There can be no ques- 

 tion of the care and accuracy with which they have been conducted j 

 and very little ground to object to the conclusiveness of the posi- 

 tion which the results demand that is, that the effect of carbonate 

 of lime, acting through the roots of the plants, enabled them to 

 absorb and to assimilate at least more than a doubled quantity .-of 

 carbon, and consequently to disengage more than a doubled quan- 

 tity of oxygen gas, formed by the decomposition of the carbonic acid 

 taken in by the plants. The only apparent defect in the process 

 is one which is unavoidable. This is, that the wheat (or other) 

 plants were made to grow with their roots in water, a situation 

 contrary to their nature and wants; instead of in dry soil, con- 

 formable to both. But in naming this unavoidable defect, I do 

 not mean to convey that it can invalidate the results of the experi- 

 ments, or even reduce their measure in any very important extent. 



But there is one deduction which Dr. "Wight seems to have 

 made, to which it is scarcely necessary for me to announce my 

 dissent. While I fully admit that he has first indicated, and at 

 least gone far to establish by his experiments, one of the very im- 

 portant properties and powers of calcareous earth, as a fertilizing 

 manure (and also as a sanitary agent), still I do not agree that this 

 is its sole or even the most important mode of operating, for 

 either end. 



The bearing of Dr. Wight's experiments on the effect of calca- 

 rferdus manures in preserving health, will be referred to when that 

 subject shall come under consideration. All reference to this 

 branch of the subject in this chapter was incidental and in advance 

 of the designed and more appropriate place. 



The power given by calcareous earth to plants to draw carbonic 

 acid much more copiously from the atmosphere, which Dr. Wight 

 so admirably deduced from actual experiments, might previously 

 have been inferred from the observations of alleged facts made by 

 practical cultivators. But the statement, hidden in the German 

 of the agricultural chemist Sprengel, probably first was disclosed 

 in this country in the recently published " Lectures" of Johnston, 

 whose words I will quote. This author, referring to Sprengel, 

 says : " He states that it has very frequently been observed in 



