1816.) On the Physical Analysis of Soils. 215 
state of purity on the growth of plants. I propose to communicate 
to the public in the fifth number of the Feuilles Economiques of 
Hofwyl, the subsequent details of all these experiments, with their 
particular relation to rural economy. 
; G. Scuiisuer. 
ARTICLE VY. 
Vindication of Mr. Dalton’s Theory of the Absorption of Gases by 
Water, against the Conclusions of Saussure. By Mr. Joha 
Dalton, 
(To Dr. Thomson.) 
RESPECTED FRIEND, Manchester, Jan. 22, 1816, 
In the Annals for November I find a paper by M. de Saussure on 
the absorption of the gases by liquids. 1] read it with some interest, 
as a subject which engaged my attention pretty fully some years ago, 
and-which indeed I have never since lost sight of. It gave me 
great surprise that the conclusions I deduced from my experiments 
should have been so far misunderstood by so acute and able a writer 
as Saussure, and I flattered myself that his readers could scarcely fail 
of seeing that his animadversions on what he calls my theory of the 
absorption of gases are in great part misapplied; unless it be assumed 
as an axiom, that if from equal measures unequal measures be 
taken there will remain equal measures. But when I find you 
have translated the Essay without discovering the misapplication, 
and two months afterwards reviewed the same, and still seemed to 
remain in ignorance, I fear that my deductions must have been 
stated in such way as not to be easily understood, at least by the 
generality of readers who may be said to run and read. 
When water deprived of all air is agitated along with a given 
volume of any gas or mixture of gases, and at the same time sub- 
ject to a given pressure as that of the atmosphere, after a few 
minutes an equilibrium takes place, or the water having imbibed a 
certain quantity ceases to imbibe more of the gas. Now my 
hypothesis is, that certain uniform relations exist in regard to the 
density of the gases whether simple or mixed, in and out of the 
waters, after the process of absorption has ceased; but, it says 
nothing at all as to the relations out of the water, prior to the 
absorption. In some cireumstances the cases are indeed in effect 
the same, and no distinction is of course necessary ; as for instance, 
when water is impregnated with atmospheric air in communication 
with an unbounded volume of the air, or when the several gases 
subjected to the absorption are equally absorbable ; but in instances 
such as Saussure has given, where the volumes of gases are limited 
and unequally absorbable, the two cases are as widely different as 
