¥ Bn. 
hoe tae Use of Sulphate of Copper, &c. in Bread.. 269 
ba — 
He When ordinary plate glass is used with flint glass. whose specific 
_ gravity is 3.45, the radii previously given may be taken as the stan 
dard. If the density be 3.50, the first radius should be changed in 
the triple object glass, from 0.15 to about 0.14, applying the other 
radii, as there given, fora standard. The plate glass used had a re- 
fractive power of 1.514. iy 
In order to obtain the best forms for microscopes, it appears ne- 
cessary to make those radii which are situated at nearly the same 
distance from the focus of the microscope, as nearly equal as possi= 
ble, and atthe same time correct the color and spherical aberra~ 
tion,—as indistinct vision caused by secondary aberration of figure, 
will be produced, if the diameter of the pencil of light be too great 
in proportion to the radius of the surface through which it passes. 
Thus ‘in a triple microscope, having a double-concave flint glass 
whose radii are equal, an aperture much greater than four fifths of 
the shortest radius in the microscope, (even if its focal distance were 
made very short,) cannot be advantageously used, especially if the 
first concave surface has a radius as short as any in the microscope. 
It is believed a microscope might be made more powerful than 
any hitherto used, by substituting sapphire or some other substance 
of similar optical properties for plate glass; and using flint glass of 
great density. This would enable us to diminish the focal length in 
relation to the aperture, and thus increase the power. 
Greatfield, Cayuga County, N.Y. May, 1831. 
Arr. VII.— Considerations on the employment of Sulphate of Cop- 
per, and of various other saline materials in the making of Bread, 
Presented to the board of Health of the department du Nord, 
(April, 1830) ; by M. Kuuimann. 
(Abridged from the Annales de L’Industrie; by J. GriscoM.) 
‘Berne frequently called upon by the tribunals to undertake the 
chemical examination of bread, suspected to contain substances inju- 
rlous to health, the author obtained a variety of facts relative to, thi 
kind of adulteration, which he has deemed it right to exhibit, in order 
that those who may be occupied with such examinations, may be 
saved the trouble of numerous trials, and that the public authorities 
May direct their attention to a matter which so much concerns the 
Seneral welfare. 
Vou. XX.—No. 2. 35 
