40 



Klaproth on Mineral Stibstanees. 



Oxide of chrome 

 Oxide of iron . 

 Alumina . 

 Silica . . . . 

 Loss by ignition 



(d) 



(c) 



(M 

 (a) 



55.50 

 33 



6 



2 



2 



98.50 



Art. V, A Letter respecting the Construction of a Balance, 

 from Capt. Henry Kater*. 



London, Aug. 8th, 1821.' 

 Dear Sir, 



I OBSERVE in the last number of the Quarterly Journal, 

 edited at the Royal Institution, the description of a Balance 

 from a drawing by Mr. Children. I should not have troubled 

 you merely to claim this as my own arrangement, but to notice 

 an error in the description where the beam is said to be " of 

 platinum ; " it should have been " of bell-metal," which com- 

 bines the essential desideratum lightness with the requisite 

 degree of strength. 



This beam had its origin in a wish to render the hydrostatic 

 balance less expensive without diminishing its accuracy and 

 sensibility, and it has in every respect answered my expec- 

 tations. 



Dr. Wollaston has contrived the following additional apparatus, 

 which he finds particularly convenient. The annexed wood-cut 

 represents the bottom of the case supporting the balance, A and 

 B the scale pans. Four slips of wood, or brass, are connected 

 by pins forming centres of motion at a, b, and c, the centre c, 

 being fixed to the case. Four brass pins, e, f, g, h, of a suffi- 

 cient length, project perpendicularly from the side pieces. These 



♦ We need scarcely observe tbat we were not aware to whom Mr. 

 Robinson was indebted for the plan of the very useful balance of which 

 we have given an account in our last N umber. We merely saw the instru- 

 ment in the possession of Mr. Children, who was kind enough to furnish 

 the sketch from which our engraving was made. 



