4 THE YOUNG 
drench it freely for one or two minutes in 
clean water, and hang it up by one corner 
to dry. 
Any good hard paper may be employed 
(from even a leaf from a press copy book 
up to Bristol board) which will bear the 
necessary wetting. 
For the sensitizing solution take Ig 
ounces citrate of iron and ammonia, and 8 
ounces clean water ; and also, II ounces 
red prussiate of potash and 8 ounces clean 
water ; dissolve these separately and mix 
them, keeping the solution in a yellow 
glass bottle, or carefully protected from 
the light. 
The paper may be very conveniently 
coated with a sponge of 4 inches diameter, 
with one flat side. The paper may be 
gone over once with the sponge quite 
moist with the solution, and a second time 
with the sponge squeezed very dry. The 
sheet should then be laid away to dry in a 
dark place, as in a drawer, and must be 
shielded from the light until it is to be 
used. When dry, the paper is of a full 
yellow or broDze color ; after the exposure 
to the light, the surface becomes a darker 
bronze, and the lines of the tracing ap- 
pear as still darker on the surface. Upon 
washing the paper, the characteristic 
blue tint appears, with the lines of tracing 
in vivid contrast. 
It will readily be seen that the process 
is strictly photographic in the ordinary 
sense of the word— the tracing taking the 
place in the printing of the ordinary glass 
negative. Hence, all details are closely 
reproduced, even to the texture or threads 
of the tracing cloth. 
A working drawing thus made furnishes 
its own background, and does not require 
to be placed over a white ground, as is 
often the case with a tracing. If desired, 
the copy can be made upon common bond 
paper, which can be mounted upon a board 
in the usual way. 
Inasmuch as such copies can be made 
from tracings only, it may be well to sug- 
gest, and urge, that drawings can be com- 
pleted, or nearly so, in i)encil upon paper 
in the usual way, and that all the inking 
can be done upon tracing cloth laid upon 
the pencil-work. In this way the cost of 
the tracing (in the ordinary sense) can be 
SCIENTIST. 
wholly saved, and the single copy of the 
finished tracing can thus be made in the 
"blue" way, to the best possible ad- 
vantage. 
It may safely be said that this method 
of copying can be employed, if only one 
or two copies per week are needed of 
ordinarily complex drawings, with excell- 
ent results, and with a very important 
saving of both time and money. 
A ready means of adding to or correct- 
ing the blue copies may be found in the 
use of a solution of carbonate of soda or 
potash, used with a pen or brush. 
A Home Made Chuck. 
A CHUCK for small lathes, made after 
the following plan, does not cost much 
for material or time, and will be found 
very useful: 
A is a piece of brass to screw on the 
mandril. It has an external screw on the 
outer end to receive the brass cover b. 
The inside of the outer end of b is conical, 
and c is a piece of wood turned to fit it. 
When B has been screwed down tight, a 
A SIMPLE CHUCK. 
hole the size wanted is turned in c, and a 
saw cut or two are made as at d. This 
allows the hole in c to close, and after the- 
article has been inserted, by screwing b 
on A, it may be held tightly. Little 
blocks like c are easily turned, and a few 
of them serve for a wide range of sizes. 
—A novel Art College for Women has- 
been established near Wimbledon, Eng- 
land, by Miss Bennett, a lady well known 
for the gratuitous instruction she has been 
in the habit of giving in art needlework. 
The course of study is thorough and com- 
prehensive and the fees are moderate. 
The students will have the opportunity of 
getting renumerative employment, if 
needed. 
