On the Production of Carbonic Acid from Manures. 503 



tity of carbonic acid produced could be estimated. This consisted 

 of a large bell-jar fitted wdth a cork, and cemented down to a 

 glass plate so that it could be made quite air-tight. The cork 

 had two tubes, through one of which air freed from carbonic acid 

 by bubbling through potash and carbonic acid, passed ; the other 

 tube communicated with two vessels containing baryta-water to 

 absorb the carbonic acid produced, and with the aspirator, by 

 means of which air was drawn through the apparatus. The ex- 

 periments were made by placing the substances under the bell- 

 jar, making it air-tight, and then drawing air through at the rate 

 of about five gallons in six hours. The experiments generally 

 lasted twenty-four hours, and at the expiration of that time the 

 carbonate of baryta was collected and weighed. 



In one experiment, a fiower-pot containing garden-mould which 

 had not been manured for a long time, was placed, and the 

 aspirator set in motion. After twenty-four hours the carbonate 

 of barjfta was collected and weighed. The layer of mould was 

 about 18 inches square and 3 inches deep, and the quantity of 

 carbonic acid produced was such as to show that a hectare of 

 land (about 2^ acres) would produce in the course of twenty-four 

 hours 500 hectolitres (or about 11,000 gallons) of carbonic acid. 

 A similar experiment with a more clayey soil gave 300 hecto- 

 litres of carbonic acid for a hectare of land. The same soil turned 

 up with a knife, so as to imitate the effect of ploughing, gave a 

 quantity of 400 hectolitres for the hectare. 



An experiment was made with soil taken from a field of beet- 

 root, which had had farm-yard manure in winter, and colza tops 

 in March. The experiment lasted four days, at a temperature 

 varying from 20 or 25 to 30 or 35 degrees, but it did not 

 appear that the temperature had much influence on the result. 

 It was found that the quantity of gas gradually decreased from 

 day to day : the mean result corresponded to a quantity of 1570 

 hectolitres per hectare, or about 13,800 gallons per acre. 



These results prove that a very large quantity of carbonic acid 

 is produced in a field cultivated and well manured, and that the 

 mass of this gas is assimilated directly by the leaves of plants, 

 for it is not conceivable otherwise how there could be such a 

 small proportion in the air. 



Corenwinder also made a series of experiments with manure. 

 He found that a layer of fresh cow-dung exposed, under the con- 

 ditions indicated, at a temperature of about 20°, gave a quantity 

 of carbonic acid equal to 1240 hectolitres per hectare. Cow- 

 dung kept four days, which was in a state of change, and then 

 submitted to experiment, gave in twenty-four hours carbonic acid 

 at the rate of 2000 hectolitres per hectare, or 17,600 gallons 

 per acre. At a temperature of 20°, fresh horse-dung gave results 



