and Peat-charcoal for Agricultural purposes. 177 



experiments were very diflferent from those in the experiments 

 described in this communication. 



De Saussure, who appears to have made the most extended 

 researches on this subject, when he ascertained that charcoal 

 absorbed about ninety times its volume of ammoniacal gas, em- 

 ployed perfectly dry and very dense charcoal made from boxwood 

 (the denser the charcoal the greater its absorbent power), and in 

 order that it might be as free as possible from air, heated the 

 charcoal red-hot, and while in this state plunged it under mer- 

 cury and thus cooled it out of the contact of the air, and after- 

 wards let it up into the gas. Such perfectly dry charcoal, and 

 so free from aii-, could never occur in practice, and are not the 

 conditions in which charcoal is placed when used as a deodorizer 

 of animal excreta, &c. ; for in addition to its having absorbed 

 much air and moisture from the atmosphere in spite of the most 

 careful mode of keeping, it becomes more or less completely wet 

 on mixing it with excrementitious matters ; and the experiments 

 of De Saussure show that the absorbing power of charcoal for 

 different gases is greatly impaired by the presence of moisture. 

 It appeared, however, interesting to me to ascertain what was 

 the relative absorbent power of peat-charcoal, thoroughly dried 

 peat, and of that in its ordinary state of dryness for ammoniacal 

 gas. For this purpose I selected a good and tolerably dense sod 

 of peat or tm-f, and having converted a part of it into charcoal, 

 I made three small cubes of the same size as nearly as possible, 

 one out of the charcoal, and two out of the uncharred part, one 

 of which I then thoroughly dried by exposing it for many hours 

 to a temperature of 21 2° F. The cube of charcoal, that it might 

 be as nearly as possible under the same conditions in respect to 

 dryness and absorption of air as the cube of dried peat, I left 

 exposed to the air for some time and afterwards dried it at 212° F. 

 The third cube was left in its ordinary state of dryness, which 

 was found by drying another portion of the sod to contain about 

 20 per cent, of water. These cubes were then let up into gra- 

 duated receivers filled with ammoniacal gas standing over mer- 

 cury, and the following are the results of their absorption, the 

 volume of charcoal or peat being taken as unity. 



Absorption of Ammoniacal Gas. 



Volumes. 



Peat-charcoal 18-4 



Peat dried at 212° F 33-2 



Peat in its ordinary state of dryness"! -^.^ 

 containing about 20pcrcent. of water j 



As the weight of the cube of peat-charcoal to that of the cube 

 of dried peat in this experiment was in the ratio of 13 to 166, 



