Analytical Chemistry. 419 
Should an insoluble, heavy, gray residue remain on treating with acid, 
it must be collected and its weight deducted from that of the borate of 
magnesia. It is platinum. 
The subjoined example illustrates the method and demonstrates that 
alkali-chlorids in large excess have no serious influence on its accuracy. 
‘764 grm. of pure borax, containing 0-280 grm. of boric acid were 
dissolved with 2 grm. of chlorid of sodium and 3-2 grm. of crystallized 
chlorid of ammonium-magnesium were added. 
First residue = 0°5720 ; yea : 
contained magnesia = 0-3053 - contained boric acid = 0°2667 grm. 
Second residue = 0°1040 dé “ “« = 90093 « 
contained magnesia = 0°0947 { er 
Third residue = 0:0645 i « &€ — 9.9099 « 
contained magnesia = 0°0625 a "i 
Total, 0°2780 
Other determinations gave results of equal accuracy. From insoluble 
compounds the boric acid is obtained in solution by fusing with thrice 
their weight of carbonate of soda and exhausting the mass with water. 
or ammoniacal solution of chlorid of calcium. The precipitate of Ca Fl 
Process (except that no fusion was made), 0°1883 
0:1362 erm. of boric acid. In the analysis of borofluorid of potassium 
a loss of fluorine equal to 1:5 to 1°8 per cent occurred which Marignac 
thinks might have been avoided by employing a caustic alkali in the 
fusion. Wed. 
Pxrotocrarny.— 
8. Collodion—We translate from La Moniteur de la Photographie 
for February 15th, 1863, the following letter addressed to the editor by 
_ A. Jeanrenaup. Mr. Jeanrenaud is a well-known skillful amateur pho- 
_ tograph 
pher. 
' “Mr, Editor :—If you and several other psec had not requested 
= results I have obtained, that it will be useful.to make my formula 
__ known to your readers, I do it with the more pleasure, as T hope 
_ ‘hat those who shall take the pains to try it will have no reason to 
