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May 29, 1873] 
NATURE 85 
Clerk-Maxwell’'s Kinetic Theory of Gases 
Your correspondent, Mr. Guthrie, has pointed out an, at first 
sight, very obvious and very serious objection to my kinetic 
theory of a vertical column of gas. According to that theory, a 
vertical column of gas acted on by gravity would be in thermal 
equilibrium if it were at a uniform temperature throughout, that 
is to say, if the mean energy of the molecules were the same at 
all heights. But if this were the case the molecules in their free 
paths would be gaining energy if descending, and losing energy 
if ascending. Hence, Mr. Guthrie argues, at any horizontal sec- 
tion of the column a descending molecule would carry more 
energy down with it than an ascending molecule would bring up, 
and since as many molecules descend as ascend through the sec- 
tion, there would on the whole be a transfer of energy, that is, 
of heat, downwards ; and this would be the case unless the 
energy were so distributed that a molecule in any part of its 
course finds itself, on an average, among molecules of the same 
energy as its own. An argument of the same kind, which occurred 
to me in 1866, nearly upset my belief in calculation, and it was 
some time before I discovered the weak point in it. 
The argument assumes that, of the molecules which have 
encounters in a given stratum, those projected upwards have the 
same mean energy as those projected downwards. This, how- 
ever, is not the case, for since the density is greater below than 
above, a greater zumder of molecules come from below than from 
above to strike those in the stratum, and thereforeagreater number 
are projected from the stratum downwards than upwards. Hence 
since the total momentum of the molecules temporarily occupying 
the stratum remains zero (because, as a whole, it is at rest), the 
smaller number of molecules projected upwards must have a 
greater initial velocity than the larger number projected down- 
wards. ‘This much we may gather from general reasoning. It 
is not quite so easy, without calculation, to show that this differ- 
ence betwen the molecules projected upwards and downwards 
from the same stratum exactly counteracts the tendency to a 
downward transmission of energy pointed out by Mr. Guthrie. 
The difficulty lies chiefly in forming exact expressions for the 
state of the molecules which instantaneously occupy a given stratum 
in terms of their state when projected from the various strata in 
which they had their last encounters. In my paper in the 
Philosophical Transactions, for 1867, on the ‘‘ Dynamical Theory 
of Gases,” I have entirely avoided these difficulties by expressing 
everything in terms of what passes through the boundary of an 
element, and what exists or takes place inside it. By this 
method, which I have lately carefully verified and considerably 
simplified, Mr. Guthrie’s argument is passed by without ever 
becoming visible. It is well, however, that he has directed 
attention to it, and challenged the defenders of the kinetic 
theory to clear up their ideas of the result of those encounters 
which take place in a given stratum. J. CLERK MAXWELL 
Additional Remarks on Abiogenesis 
SINCE my communication in NATuRE, March 20, a further 
investigation of the subject has shown me that the experiments 
there recorded do not yet fully prove the reality of abiogenesis. 
My argumentation based on those experiments is liable to the 
following objection :— 
The Pepe experiment (water, potassium-nitrate, magné- 
sium-sulphate, calcium-phosphate, glucose, and peptone) is 
conducted in a zextrva/ solution. In the control-experiments 
neutral ammonium-tartrate is used as nutritious substance for the 
supposed germs. But this salt disassociates by boiling, loses 
ammonia, and the reaction becomes acid. When, therefore, 
Bacteria appear in the principal experiment and not in the con- 
trol-experiments, this result can be explained by admitting that 
the germs resist a temperature of 100° in a neutral liquid, but 
are killed by the same temperature in an acid solution. This 
explanation agrees very satisfactorily with the fact proved by 
Pasteur, that an acid reaction is much more deleterious to living 
germs than a neutral reaction at the same temperature. 
This objection is very rational, but it does not throw over my 
conclusion respecting the reality of abiogenesis, for the following 
reasons :— 
It is now obvious that in the control-experiments ammonium- 
tartrate cannot be used, a nitrogenous body must be sought, 
not too complex, that remains neutral by 100°. For this end 
I have found urea to answer well. Pure urea is perfectly fit to 
furnish nitrogen to the Bacteria, but not to furnish them their 
carbon, Bacteria sown ina solution ofurea and mineral sa'ts do 
not develop themselves, but when sugar is added their growth 
goes forth rapidly. The following solution—roo c.c. water, 
0°2 grms. potassium-nitrate, 0°2 grms, magnesium-sulphate, 004 
gtms. calcium-phosphate, 1 grm. glucose, 0°5 grm. urea, is emi- 
nently fit for the development of Bacteria. Also a solution that 
contains, instead of the sugar and the urea, o°s grm. peptone. 
These solutions were now used in the control-experiments. 
For instance : 
a. Principal experiment. 100 c.c. salt-solution,* 2 grms. 
glucose, 0°3 grms. peptone boiled and treated in the ordinary 
manner (See NATURE, vol. vii. p. 380). On the third day the 
liquid contains countless swarms of Bacteria. 
4, Control experiment. 100 c.c. salt solution, 1 grm. glu- 
cose, 0'5 grm. urea, boiled exact. No Bacteria appear; on the 
eighth day the liquid is perfectly clear. 
¢. Control experiment. 100 c.c, salt solution, 05 grm. pep- 
tone, boiled, &c. On the eighth day complete absence of 
Bacteria. 
In each of these experiments the reaction is neutral. They 
are therefore fully comparable. The experiments 4 and c prove, 
moreover, that the closing tiles exclude completely the atmo- 
spheric germs, a fact that was also proved by direct experiments, 
wherein the solutions 4 and ¢ were used and dust strewn on the 
closing tile in the manner formerly described. 
But is it not possible to generate Bacteria in a liquid which 
has been boiled when acid? 
To elucidate this point, the above-named solution a was ren- 
dered acid (2-4 c.c. of a 1 per cent. solution to 100 c.c.) and 
treated as usual. No Bacteria appeared, whether the liquid was, 
after boiling, neutralised with soda or not. 
But this negative result is easily conceivable ; for the acid alters 
essentially the calcium-phosphate, changes CaHPO, into Ca,H, 
P,Og. And that this alteration is not without influence, is rendered 
probable by the fact, which I have recorded in the Maandblad 
voor Natuurwetenshcappen, No. 7 (April 23, 1873), namely, 
when in the principal experiment instead of CaHPO, is used a 
mixture of Ca,P,O,, and Ca,H,P,Oy the result (the genesis of 
Bacteria) is much less constant. The neutral calecium-phosphate 
by boiling with water breaks up in the basic and the acid salt, 
but this division must take place in the presence of sugar and 
peptone. 
On the other hand, the acid modifies the peptone. This is 
easily demonstrated by comparing, in the polariscope, the rotating 
power of a neutral peptone-solution with the power of the same 
solution. After boiling with acid a notable difference is ob- 
served. 
The acid can, nevertheless, be employed with the following 
modification :—In 100 c.c. water are dissolved 0°2 grm. potas- 
sium-nitrate, 0°2 grm. magnesium-sulphate, and 2 grms. glu- 
cose ; 2 c.c. of a 1 per cent. solution of tartaric acid are added, 
so that the liquid has a strong acid reaction. It is then boiled 
for ten minutes. Then with a red hot platinum spatule a little 
soda is taken from a hot crucible and thrown in the flask. The 
quantity of soda required is approximately ascertained by a pre- 
liminary trial. Care should be taken not to render the liquid 
alkaline. Then 0’05 grm. calcium phosphate and 0°3 grm. 
peptone are added together, and the boiling continued for ten 
minutes. The flask is closed as usual, and deposited in the 
hatching-bath, Three days after, it swarms with Bacteria. 
When, instead of calcium-phosphate and peptone, are added 
0°05 grm. calcium-phosphate and 0°5 grm. urea, nothing ap- 
pears ; and the result is equally negative when the following sc« 
lution is taken :—100 c.c. water, 0'2 grm, potassium-nitrate, 
o’2 (grm, magnesium-sulphate, o'05 grm. calcium-phosphate, 
I grm. potassium-natrium-tartrate, 0°3 grm. peptone. In this 
latter case no acid is used. The addition of the tartrate is made 
to have a sufficient quantity of carbon in the liquid. These con- 
trol experiments prove that none of the employed materials, 
neither the glucose, nor the calcium-phosphate, nor the peptone 
did introduce germs. ; 
By these experiments the above-stated objection is, in my 
opinion, satisfactorily refuted. ‘ ‘ 
In concluding these remarks, I must mention an important 
fact. For the above-described experiments, I employed mostly 
the ordinary glucose, an amorphous, yellowish white mass, not 
chemically pure. By crystallisation from strong alcohol, I puri- 
fied this sugar. In three different preparations I obtained thus 
three samples of perfectly white more or less pure glucose, One 
* Composed of 1 grm. potassium-nitrate, 1 grm magnesium sulphate, o°z 
grm, neutral calcium-phosphate in 500 ¢.c, waters 7 
