Chemistry and Physics. 99 
tine from the protochlorids as from the perchlorids of tin and copper. 
But we obtain in this way from the protochlorids twice as much metal 
with the same current as from the perchlorids. 
(11.) The same force is also necessary to obtain equal quantities of 
oxygen from a solution of iodic acid and from dilute sulphuric acid whic’ 
are decomposed in separate vessels. In this case however onl fth 
of an equivalent of iodine is obtained for one equivalent of hydrogen 
separated from the sulphuric acid. 
(12.) Faraday’s law is applicable in its fullest extent inasmuch as 
equivalent quantities are always separated from complex saline com- 
pounds. But the galvanic are not the same as the chemical equivalents. 
_{13.) Saline particles change their position in eletrolytes partly by con- 
tinual decompositions and recombinations, partly by diffusion. The den- 
sity of the solution exerts a sensible influence upon the diffusion, which 
1s however different in different saline solutions—Ann. der Physik und 
Chemie, cii, 52. 
2. On the influence which metals exert upon radiant heat—Knopiavcn 
has communicated a memoir upon this subject the most important results 
of which in the author’s own words are as follows. 
(1.) Metals like gold, silver, and platinum in thin plates are to be re- 
garded as diathermanous bodies, which allow a portion of the rays of 
heat to pass through, which portion diminishes more and more with in- 
creasing thickness of the metal. : 
this transmission certain metals, for example gold and silver, exert 
an elective absorption upon the rays of heat analogous to that of trans- 
Parent colored bodies upon rays of light; while others, like ! 
. 
partly absorb and partly transmit ath kinds of rays of heat ‘ee an opal 
r 
i ig as is the case with transparent colorless bodies with respect 
: i 
Rays of heat, according to the foregoing statement, exhibit, after their 
Passage through the metals of the first class, different relations, with re- 
th ge through diathermanous bodies, from 
those which they show before their entrance into these, and this peculiar- 
uy 'S expressed more distinctly in proportion as the metallic layer pas 
through is thicker. In metals like platinum this thickness exerts no in- 
hee on the quality of transmitted heat. 
These last would behave like gray substances with respect to the “T 
of heat as well as toward the visible rays. Substances which can 
Compared with those which are transparent and white with respect to 
M eonsequence of which this becomes changed in its properties. Others 
on the contrary, platinum, iron, tin, zinc, lead, alloys of lead and tm, 
and german silver, reflect all kinds of rays of heat in equal proportion, 
