270 Correspondence of J. Nicklés. 
evaporation of water :—(5), after the roasting is thus completed, the 
material is removed to the boilers, to undergo five treatments success- 
ively with boiling water, in order to extract all the chromate of potash, 
using the last waters with a new supply of the roasted ore; if there is 
some chromate of lime in the liquid it is precipitated by means of car- 
bonate of potash :—(6), the solution of chromate of potash is concen- 
trated to one-third of its original volume, one-half of the potash of the 
chromate is saturated with sulphuric acids which allows of a separation 
at once of the bi-chromate from the insoluble sulphate of potash which 
is precipitated ; then the concentration is completed before conducting 
iquid to the vats for crystallization. aaa 
. Jacquelain expects considerable profit from this process, obtaining 
425 francs for 500 kilograms of the bi-chromate, which amount may 
be manufactured in one day. To 100 kilograms of ore, 45 p. c. 1D pu- 
photography to zoological studies. A. very successful attempt has bee 
made by MM. Rousseau, naturalist attached to the Museum, M. Deve- 
and of man. As photography thus gives us economically what cou 
ters. 
On learning the death of Arago, a French photographer, M. Claudet, 
established for some years in London, recalled his having taken 1D 
1843, some Daguerreotypes of this philosopher, M. Claudet, aided by 
M. Lerebours, has taken from different positions pictures from t 
guerreolype, such as may be used with a stereoscope; and we om 
have a stereoscopic picture of the man who may be said to have a¢ 
t) 
e de St. Victor, of whom we, have spoken in the number 
for November last, proposes to extend the use of his new process oP 
glass, and operate with it as for an engraving on steel. When the plate 
~ has received an impression, he submits it to the vapors of fluohydri¢ : 
acid or else pours upon a little of the liquid acid ; in the first cases" — 
engraving is unpolished, in the second, it is deep and ' ; 
