SHORT NOTES ON PROFESSIONAL SUBJECTS. 
14 
the lines, dots, &c., by which the drawing is represented ; 3 oz. of the best gelatine 
are dissolved in 40 oz. of hot water, and 2 oz. of bichromate of potash in 10 oz. of 
hot water; the two are mixed together and kept liquid while in use by means of a 
hot water dish. The paper, of a thin tough description, is coated but once with a 
mixture by being floated on it for about five minutes, and after drying spontaneously 
is hot pressed to give it a smooth fine surface. 
The drawing to be reproduced is stretched on a board and a photographic 
negative taken of it in the usual way; perfect transparency should be carefully 
maintained in the lines, &c. A sl^eet of the prepared paper is then placed under 
the negative in an ordinary pressure frame and printed in a subdued light. 
A very thin layer of lithographic re-transfer ink is rolled on a clean polished stone, 
and the print is laid face downwards on it and passed through the press; on removal 
it is placed in a dish of rather hot water and allowed to soak until the black ink 
yields to the touch, the water is then poured off and a supply of hot gum water 
added with which by means of a clean soft sponge the face of the print is washed; 
the black ink on the soluble parts of the composition, or those unaltered by light, 
are rubbed away leaving the drawing behind. Several changes of warm water are 
necessary to remove the gum and dirt, and a soft sable brush used (while the print 
is still immersed in the warm water) to cleanse out all the minute details and 
brush away whatever scum of ink remains. 
When dried it is damped on the back and laid face downwards on a slightly 
warmed polished stone, and passed once only through the press; it is then worked 
up as an ordinary transfer and may be printed in the same manner and to the same 
extent as ordinary drawings on stone. 
The negatives are taken in the Photographic Department of the Eoyal Arsenal, 
all the other parts of the process are performed in the Eoyal Carriage Depart* 
ment. 
The whole of the large series of lithographs produced in the Eoyal Carriage 
Departmdht are in course of being reduced to a smaller size by this process, a 
specimen of which can be seen at the E.A. Institution. 
Cost of small size (coloured) 3d. each. 
20. Experiments on the penetration oe iron armour plates by steel 
and chilled iron projectiles.* The steel shot were all hemispherical headed, 
and the chilled shot ogival headed. 
It requires about 28ft. tons per inch of shots circumference to send either a 
hemispherical headed steel or an ogival headed chilled shot through a 4-| inch 
unbacked wrought-iron plate. About 42 ft. tons per inch are required for a 
5-|- inch plate. 
From these experiments the following practical conclusions may be drawn when 
the projectiles are fired direct. 
(1) An unbacked wrouglit-iron plate will be perforated with equal facility by 
solid steel shot, of similar form of head, and having the same diameter, provided 
they have the same vis viva on impact; and it is immaterial whether this vis viva 
be the result of a heavy shot and low velocity, or a light shot and a high velocity, 
within the usual limits of length, &c. which occur in practice.f 
* Recently carried out under the direction of the Ordnance Select Committee, and are referred 
to in a “ Report on the penetration of armour plates by steel shot, Sfc. by Capt. W. JEC. Noble, R.A. 
London, Longman and Co. 
f If the elongated shot be of excessive length this comparison will not hold good, as there will 
be a waste of “ work” in altering the dimensions of the shot itself; 2‘25 diameters is about the 
limit of length. 
