104 
POPULAR SCIENCE REVIEW. 
was of the strength of forty grains to the ounce, and was acidified with nitric 
acid. The iron-developing solution was weak ; and the plates were fixed in 
hyp ^sulphite of soda. 
New Alkaline Dry Process . — A new dry process, which has been worked 
out by Mr. F. Maxwell Lyte, and has been lately published, possesses the 
following advantages over many of those hitherto used : — The negatives are 
characterised by great fineness, with delicacy of detail, and a total absence of 
stains ; the plates are prepared with great rapidity and in an ordinary negative 
silver bath ; and, lastly, they keep well even in the most sultry weather. 
To prepare the plates, coat with collodion and sensitise them in the usual 
bath, and wash first in water, next in common salt and water, and, lastly, 
in plain water again. Now coat them with the preservative solution 
which is composed of 
Albumen . . . 2 parts 
Water . . . . 2 „ 
Spirits of wine . . 1 part. 
The spirit must be mixed with the water previous to its being added to 
the albumen. After being whipped together and strained, when about to 
be used a sufficient quantity of this is mixed with a sixteenth portion of 
its bulk of ammonia saturated with chloride of silver. 
When the plates have been coated with this preservative they are 
thoroughly dried and stored away till required for use. The development 
is effected by a plain one per cent, solution of protosulphate of iron, by which 
the image will be rendered very faintly visible ; but any degree of intensity 
mav be obtained by a subsequent application of pyrogallic acid and silver. 
Removal of Silver Stains . — Many methods for the removal of stains from 
the fingers of the photographer have been published, but the latest dis- 
covery in connection with this subject will probably prove to be not the 
least valuable, seeing that no cyanide of potassium is required : — Immerse 
the fingers in a saturated solution of sulphate of zinc slightly acidulated, 
and then rub the stains with a bar of metallic zinc, in order to facilitate the 
reduction of the silver or iron of which the stains are composed. The salts 
of zinc and iron which have penetrated the skin are decomposed by the 
zinc salt, and all the zinc salts are white and soluble. When the last trace 
of black has disappeared, the hands are first rinsed in plain water and then 
washed in soap and water. 
A Portable Camera for Dry Plates . — Photographic tourists are now likely 
to get a camera in which are combined all their requirements. A patented 
instrument has been exhibited, and is now being manufactured, capable of 
containing a camera and lens, twenty-one sensitive plates ready for ex- 
posure, and all other requisites, the whole size being eight inches high by 
five inches deep. The chief peculiarity of its construction is that the lower 
portion of the cabinet contains the sensitive plates, which, by the action of 
two handles, are each brought up to be exposed in the camera, and after- 
wards stored away, permitting each plate of the whole series to be thus 
treated with a degree of certainty from which no hitch can be anticipated. 
It has secured the admiration of all who have seen it, and is likely to come 
into general use during the next season. Mr. Walter Cook is the inventor 
of this ingenious camera. 
