THOMSOI^’S EXPERIMENTS IN CALICO-PRINTING. 
141 
and the same side of the cube under the 
pyramid, form part of the perspective of 
this parallel surface. The point where 
the line let fall from point h in the 
ground plan, perpendicular to the line « 6 
in the perspective view, cuts the line o c, 
is the perspective of the bottom corner at 
of the cube A ; and the place where 
this same line lip cuts the perspective 
line n e, is the perspective of the top corner 
g^ of the cube marked A, in fig. 1. So now 
we have got the perspectives of the four 
corners of one of the sides of the cube in 
front of the picture, and by joining these 
corners we get the surface np, and this 
smface is the perspective of the side of 
this cube, that is, towards the object D. 
A perpendicular, let fall upon the line a h, 
in fig. 2, from the point/, in the ground 
plane will cut the lines n-c and o e, so as 
to give the perspectives of the top and 
bottom corners at e of the cube under the 
pyramid ; and the other two corners of the 
side of this cube, that is, next the object 
C, is obtained in a similar manner. The 
manner of demonstrating what has been 
said in this paragraph about the perspec- 
tives of lines running perpendicular to the 
picture-sheet, from any point in it, to an 
indefinite distance from their commence- 
ment, is shown in paragraphs 3 and 4. 
Before proceeding farther, it may be as 
well to turn over and read remarks 2, 4, 
and 6. 
6. We now know how to find the per- 
spective of any point in a line that stands 
perpendicular to the transparent plane ; but 
if the perspective of a point, which is not 
in a line so situated, be wanted, we can draw 
a line perpendicular to the picture-sheet 
through the point, (or suppose a line so 
drawn,) and find the perspective of the 
point, as if it had its place in this line. 
The following rule to find the perspective 
of any point in an object, rests upon this 
principle. When the perspectives of all 
thepoints in an object are found, the perspec- 
tive drawing of the object is completed by 
joining these perspective points. 
To he continued 
ON CALICO-PRINTING. 
By Thomas 1’iiomson, M. D., F. R. S. 
L. and E. &c. &c. 
Itegius Professor of Chemistry in the 
University of Glasgow, 
(Continued from f age 104.) 
2. MADDER PURPLE.— The iron 
mordant thickened in the same way as the 
alum mordant, is similarly applied. The 
cloth is then exposed to the air for a few days, 
and the iron fixes itself on thecloth in propor- 
tion as it becomes peroxidized. The piece is 
then cleaned and washed as described in the 
last process, dyed in madder, and cleared in 
the same way as in the red just described. 
The depth of the purple depends upon the 
strength of the iron mordant. If its specifiio 
gravity be as high as 1*04, it forms a black, as 
appears in the three succeeding specimens. 
3. This piece shows two different shades 
of purple, or rather black and purple along 
with red, all dyed at once. The black and 
purple are printed together by the cylinder 
machine, with two copper rollers, and the 
purple is printed afterwards by the block. 
4. COCHINEAL PINK.— After the 
black in this pattern has been produced in 
the way already detailed, it receives an alum 
mordant on those parts which are intended to 
become pink. It is then cleansed and dyed in 
cochineal in a similar way as when cloth is 
dyed with madder. The cochineal does not 
tinge the ground as madder does ; and there- 
fore, does not require, nor is it of sufficient 
permanence to bear the same clearing opera- 
tions. So much colouring matter does the 
cochineal insect contain, that one ounce is suf- 
ficient to dye fifteen or twenty yards of such a 
pattern, as No. 4. 
5. LOGWOOD BLACK.-The same 
alum mordant which forms a red with madder, 
becomes black when dyed with logwood. The 
iron mordant has the same property ; but it 
forms a brownish, and less pleasing colour. 
Rincing the piece of goods in hot bran and 
water, is sufficient to remove the tinge of log- 
wood from the white ground. 
6. The two shades of colour in_No, 6, are 
obtained from mixed alum and iron"mordants, 
dyed in a mixture of madder and quercitrspn 
bark. The mode of producing the black and 
white figures on it, will be explained after- 
wards. 
7. PRUSSIAN BLUE.— The iron mor- 
dant is applied, and the cloth cleansed in 
the way already described. It is converted 
into Prussian blue of various hues, by immer- 
sion in cold prussic acid. This acid is libe- 
rated from a weak solution of prussiate of 
potash, by an equivalent of sulphuric acid. A 
more convenient process for this colour, is 
now employed, and it will be explained, when 
we come to speak of steam colours. 
8. BUFF FROM IRON.— This pleasing 
colour is merely the peroxide of iron. A 
mixture of sulphate of iron and acetate of lead 
is printed on the cloth, constituting in fact, 
sulphate and acetate of iron together. After 
exposure to the air for a considerable time, to 
produce as large a deposit as possible upon 
thecloth, the iron is farther precipitated by 
immersing the piece in thick lime water, or 
in a mixture of caustic potash and lime. A 
portion of black oxide is thus thrown down 
along with the red, which speedily changes 
in the fresh water and air to which it is after- 
wards exposed. 
9. MANGANESE BRONZE.— A solu- 
tion of sulphate of manganese is printed on 
tli§ cloth by the copper I'oller. VYheudry, 
