178 Prof. Magnus's Hydraulic Researches. 



the volume of ammoniacal gas absorbed by equal weights of the 

 peat-charcoal and dried peat oughtj by calculation^ to be in the 

 ratio of about 23-4 to 33-2. 



These results show that the absorbent power of peat-charcoal 

 for ammoniacal gasj even in the dry state, is very much overrated, 

 and is much less than that of dried peat, whether estimated by 

 bulk or weight, and is far less than that of peat in its ordinary 

 state of di-yness. 



As regards carbonic acid, the great food of plants, peat has a 

 decided advantage over peat-charcoal, as the former readily un- 

 dergoes decomposition in the soil, particularly if it is in contact 

 with decomposing matter (as excrementitious substances), and 

 gives rise to carbonic acid in the soil, both to supply the wants 

 of the young plant before its leaves are sufficiently formed to 

 obtain this indispensable substance from the surrounding atmo- 

 sphere, and to render soluble in water certain earthy salts, &c. 

 required by vegetation, and present them in a state in which 

 they can easily be taken up by the roots of plants. Charcoal, 

 on the other hand, from its being so little liable to undergo 

 change, or be oxidized and converted into carbonic acid at the 

 ordinary temperature, would, uuder the same circumstances, fur- 

 nish only a very minute quantity of carbonic acid, even after the 

 lapse of a long period. 



Peat, likewise, from its greater elasticity, is better calculated 

 than peat-charcoal to improve the texture, and render moi-e per- 

 vious to the air heavy clay soils deficient in vegetable matter ; 

 and besides many other arguments which might be adduced in 

 its favour, peat in the partially dried* and coarsely-powdered 

 state in which it should be employed, would only be about one- 

 fifth, if so much, of the expense of peat-charcoal. All these cir- 

 cumstances show that peat is greatly superior to peat-charcoal in 

 manufacturing manures for agricultui'al purposes. 



XXIII. Hydraulic Researches. By G. Magnus. 



[Concluded from p. 107-] 



Jets from a cruciform aperture. 



61. TF an apertm-e be made in the form of a cross, as repre- 

 -i- sented in Plate II. fig. 17, in which the length of each 

 slit, yy^, is 40 millims., and the breadth 3 millims., then when the 

 efflux is regular, i. e. when neither a rotation of the liquid nor 

 any hindrance to the motion is present, the form will be obtained 



* The peat used iu all these experiments, except those on the absorption 

 of ammoniacal gas, contained about 28 per cent, of water. 



