Arran Baryto-Sulphate Pigment. 141 
where it is ground, below the surface of water, by the attri- 
tion of four large blocks of granite, each of which is attached 
by iron chains to the arms of a vertical axis, put in motion by 
the water-wheel. 
A stream of water is at intervals admitted into the tubs, 
and its overflow carries off the finer particles, which are col- 
lected in oblong troughs, where the water deposits the sedi- 
ment in the form of an impalpable powder. There are four 
such grinding tubs in one large room, which contains also the 
crushing apparatus. 
The collected sediment is drained and moulded into the 
form of thin bricks. These are removed to a stove kept at 
the heat of about 200°; and when dry, they are crushed, and 
packed into casks, to be sent to market. 
The works are under the direction of a very intelligent 
overseer, Mr William Morton, who has had considerable ex- 
perience in other chemical works. 
The machinery at this place is capable of making twenty 
tons of white pigment a week, or more if there were two re- 
lays of workmen: at present, with only six workmen, ten tons 
per week are produced. 
This white sulphate is ground up with oil as a paint, and is 
also mixed with white lead, to form a cheaper though inferior 
basis of a pigment. But, at this manufactory, I found that va- 
rious colours are also imparted to the sulphate ; such as blue, 
yellow, and green of various shades. The colours are either 
here ground with oil into prepared pigments, or are sent to 
Glasgow, where the colours are sold by Messrs Fleming and 
Hope, in Hanover Street. 
The dry colours are sold at the following prices :— 
Prepared White, at . : L.4, 15s. per ton. 
Blue, from . 3 . L.15 to L.20 
Ordinary Green, at. : L.20 
Finest Green, at f L.25 
I did not ascertain the price of the yellow; but it is pro- 
bably about the same as the best green. 
Of course, I did not ask how these colours were prepared ; 
but I analyzed them, and then succeeded in imitating them, 
by precipitating various colours on the prepared sulphate, dif- 
gused in water—or rather in the metallic solutions which af- 
