350 On the Refraction of Laight. 
retort is broken,* and the acid thrown into large stone ware jars and 
thus sold. The cofeothar is extracted from the retorts by means of 
the scraper; it is of a. dark red color, having occasionally a yellowish 
hue, which indicates but a partial decomposition. This oxide is sent 
back to Goslar, where it is manufactured into ochre. ‘Those of the 
‘retorts that are no longer fit for service are replaced. Twenty four 
hours suffice for collecting the acid, and making the necessary prep- 
arations for a new operation. T tie quantity of ‘sulphate of iron em- 
ployed in each charge, is always effloresced in the lateral chambers, 
by a preceding heat. ‘Thus each furnace is heated three times per 
week, leaving the workmen at liberty the seventh day. 
The depot of this acid is at Frankfort, on the Mayne ; in Paris its — 
first cost is forty sols the pound. The sulphate of iron costs 1 thaler 
and 12 bons groschens the quintal. The four furnaces consume at 
one distillation seven matters of wood, giving a quantity of acid, ac- 
cording to the manner that the distillation has been conducted, from 
200 to 260 lbs. which is sold at 15 bons groschens the pound. The 
colcothar sells for 12 bons groschens the 5 quintals. ‘The cylinders 
last a ioe long time; thus the expenses for breaking are pet 
os 
Arr. zs — Observations oan Beside on. the nkenomeni de- 
veloped by Light, in its passage through small apertures ; with re- 
marks on some of the received theories, and an investigation into 
the cause a4 pragate analysis ; by Couumsus C. COnnaMA MI 
TO THE EDITOR. 
gar experiments and observations contained in the following p2- 
per, relate to the partial decomposition which light undergoes in pass- 
ing through small orifices, and impinging on thé surfaces of bodies, _ 
and to other phenomena of vision. . Although the subject | has long 
exercised the ingenuity and industry of studious minds, the phenom- 
appear to be inconsistent with the existing hypotheses. Without 
capitulating theories, or citing the authorities by which they are 
sustained, I proceed to the statement of the following facts, happy if 
I have augmented the number of exact observations, and thus aided 
in sy degree in advancing this interesting branch of science- 
: 
Games 4 case ee 
* The lute is moistened and reserved. 
ositiiet 
