Chemistry and Phystes. 51 
isothermals marking successive gradations of temperature. (5) 
The general motions of translation and of rotation of these 
isothermals appear to follow the motions of the area of maxi- 
mum temperature which they inclose; but both central area 
and isothermals have independent motions of their own. 
On projecting the enlarged image of a sun-spot on the 
blackened surface and then bringing a hot water box, coated 
with lamp-black, near the other side of the paper, one may de- 
velop the image of the spot in red on a dark ground. A simi- 
lar method probably may serve to develop the athermic lines 
in the ultra-red region of the solar and other spectra. 
South Orange, N. J., June 11th, 1875. 
SCIENTIFIC INTELLIGENCE. 
lL CHemistry AND PHysiIcs. 
1. On the Action of a Weaker Acid on the Salts of a Stronger 
one.— The importance in chemical dynamics of the question, what 
is the condition in which several substances exist when in solution, 
has been oftener recognized than experimentally investigated. 
Bergmann advanced long ago the theory which is now generall 
possible. Among the experiments made to settle this question, 
those of Bettendorff* are perhaps the most satisfactory. By 
studying the action of light on certain solutions, he was led to de- 
cide for the view of Bergmann. UBNER and WIEsINGER, not 
rec 
‘hey differ only, apparently, in the streagth of their chemism. Ir 
the qualitative experiments, barium nitrobenzoate and free ben- 
zole acid were dissolved in a large excess of water, the solution 
being heated to 80° ©. After cooling to 14-17° the solution con- 
tained not only the substances originally dissolved, but also free ni- 
* Zeitschr. Chem., 1866, 641. 
