242 
2 Please give a formula for a good ton- 
ing bath, that will turn out good prints of 
a good color. 
3 Is there any possible way of telling 
the correct time in developing a plate? 
4 Can Velox or Dekko paper be used 
with any developer except pyro, as used 
for plates (like Eastman’s hydrochinona)? 
Percy Herman, Ft. Dodge, la. 
ANSWER. 
1. The price of sulphocyanide of ammo- 
nium is about 60 cents a pound. 
2 1 give below the 2 toning baths rec- 
ommended by the Nepera Chemical Com- 
pany for their celebrated Rex printing-out 
paper: 
SEPARATE BATH. 
Chloride of gold........ 2 or 3 grains. 
NAVEST eve Re ean ne ae Pes Cte 30 ounces. 
Acetate of soda...... 1 to 1% drams. 
Sais (el ehat treet 25 to 30 grains. 
COMBINED BATH. 
Warm water iG ..8. 042 2hee /B 
ET y90) eno ttt 8 ounces. 
Sulphocyanide of ammonium I ounce. 
Borax 
I quart. 
Acetate of leadics us 202 he 6 drams. 
Powdered salitimi <:605 see ook 2 drams 
- Pure chloride of gold ...... 6 grains. 
Gitric Acidh ogre ee ae 2 drams 
3 The development of plates should be 
carried on until all detail has come out 
sufficiently, and until the blacks are strong 
enough to produce a good dense negative. 
This can be ascertained by looking 
through the negative before a ruby lamp. 
There is no set rule as to length of time. 
It depends on length of exposure, charac- 
ter of subject, quality of plate, etc. 
4 Velox paper can be developed with 
any developer provided it is strong and 
fresh and contains just enough bromide 
of potassium to keep the whites of the 
print clear; but it is much better to use 
one of the formule recommended for this 
paper. You will find thee formule given 
given in slip enclosed with each package 
of Velox. 

USEFUL TESTS FOR PHOTOGRAPHIC IM- 
PURITIES. 
George Lurcock, in Photo News. 
In order to insure the permanence of the 
negative or positive image, it is essential 
that all chemicals pcssessing destructive 
properties be entirely eliminated from the 
print or film. The average photographer 
is content with prolonged washing, but 
the careful and exact worker will wish 
to prove conclusively the absence or pres- 
ence of anything likely to prove detri- 
mental. 
By the aid of the following tests the 
tyro can tell whether his work is ready for 
finishing. The print or plate should be 
immersed a few minutes in pure water 
contained in a white porcelain dish, with 
occasional rocking, the water being then 
tested for the suspected substance. 
RECREATION. 
Hypo can be detected in infinitesimal 
quantities by means of a drop or 2 of sil- 
ver nitrate solution, which gives a black 
precipitate, or a dark brown to pale yellow 
coloration, according to the quantity 
present. The latter tint is best seen in 
daylight. 
Mercury (in intensification)—One drop 
of a weak solution of iodide of potassium 
gives a red or orange precipitate soluble 
in excess of the test. Sulphydric acid or 
ammonium sulphydrate gives a black pre- 
cipitate. 
Lead vin combined toning and fixing). 
—Lead is tenaciously retained by paper, 
with the subsequent deterioration of the 
print. The latter should be immersed 
in weak acetic acid, which dissolves any 
lead present. “With this, iodide of potas- 
sium will give a yellow precipitate or 
bichromate of potassium an orange red. 
Iron (in platinotype and iron develop- 
ers).—This is also held by paper and 
causes yellowing of the print. Ferrocy- 
anide of potassium painted on the saine 
strikes a blue if this impurity is present. 
Alum sometimes contains iron and 
should then be rejected. A solution of 
tannic acid will indicate by a blue-black 
coloration the presence of this substance. 
Sulphur (in sulphur toning).—Charac- 
teristic odor evolved when the print is 
burnt. 
Ferrocyanides (in reducers).—Ferrous 
sulphate gives a blue, and nitrate of silver 
an orange precipitate or coloration. 
Oxalates.—A solution of calcium chlor- 
ide gives a white precipitate. 
Pyro.—Milk of lime gives a purple col- 
oration, turning to brown. 
These are the chief impurities met with, 
and these test solutions should be kept in 
little stoppered bottles in every dark 
room. The small outlay and trouble in- 
volved will amply repay the operator. At 
the same time he will train himself to do 
his work accurately and well. 
All plates should be finally varnished 
and thus protected from those chemical 
substances contained in the atmosphere, 
which slowly attack the silver image, 
and prints, bromides especially. They 
should be rendered immune by saturating 
them in a solution of paraffin wax in ben- 
zine, blotting off the superfluous liquid 
and allowing the solvent to evaporate 
spontaneously. 

HOW TO USE IT. 
Many amateurs do not use ferro-prussiate 
paper, writes R. B. A. in the English Ama- 
teur Photographer, but it is nevertheless 
worth a trial. It is convenient in getting a 
proofina hurry. Print till image assumes a 
gray metallic color, and wash well in water 
until getting a blue and white print. They 
can be rendered in a number of tints, I give 
some below: 
Sen, 
TT ° 4 
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