Uae of Sulphate of Copper, &fc. in Bread . 269 



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, for a standard. The plate glass used had a re- 

 fractive power of 1.514. 



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 at the 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. 



Art. yil. — 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 JVord, 

 (^j9n7, 1830); by M. KuhlMann. 



(Abridged from the Annales de L'lndustrie ; by J. Griscom.) 



Being frequently called upon by the tribunals to undertake the 

 chemical examination of bread, suspected to contain substances inju- 

 rious to health, the author obtained a variety of facts relative to this 

 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 

 general welfare. 



Vol. XX.— No. 2. 35 



