Miscellaneous Intelligence. 147 
The final fixation of the picture by removal of the iodid of silver has 
ives or nega 
though all collodion pictures pas of both characters, one of the two 
should always be predominan 
Of course a negative is most useful, because the drawings can be 
multiplied _— paper almost ad infinitum, but for certain objects the 
amount of detail when very delicate is inconceivably better shown upon 
glass than i paper. If then a negative picture be desired, it is best 
to develop with the pyrogallic acid solution , and — e with a solution of 
hyposulphite of soda; but if, on the ¢ contrary, a sitive picture is the 
wimaeh site the effect will be infinitely better vi eas with a bath of 
e following, viz.:— + 
Cyanid of — esley . 1 drams. 
. - pint. 
Nivea of silver, - - - 15 grains. 
The cyanid to be dissolved in the water, and the crystals of nitrate of 
silver added, which immediately cause a curdy precipitate, but this is 
than when the hyposulphite is used, but the pictures do not answ 
well for printing from. A still further intensity of the whites may be 
of iron, instead a the pyrogallic acid, ane afterwards BxIS with oo 
tion to overcome. ‘The solution is made as follo 
Proto-sulphate aR iron in ery stals, - - 1 oz. 
Water, - - by mensnre 10 oz. 
_ Sulphuric acid, - 1 oz. 
s is best used by placing ina — bath and totally immersing the 
ae which should be withdrawn the moment the picture is perfectly 
instantly plunged into a bath of plain water sufficiently copious to dilute 
the adherent moisture very considerably. The object of having the bath 
of glass, is in order to see the develo ment: of the picture, as es 
by causing a sort of fogginess to appear all over it. 
When developed with the protosulphate of iron, the pictures may be 
exposed to direct daylight before the final fixing, wm injury, in fact 
ars “— e benefit, according to Mr. Martin. 
The causes most frequently operating to prevent the success of the 
proce HE , first, want of attention to the proper i omic it is to 
this point more than any other that the utmost attention should be paid, 
and I feel confident that by well concerted measures to attain this re- 
quisite, we shall eventually be able to obtain pictures in a tithe of the 
e now necessary ; in the second place failures more often occur Irom 
er exposure than from being in too short a time 5 thissigs want of 
allowance for difference of visual and chemical foci.” 
