280 Klapvoth on Mineral Substances. 



posed of two parts of concentrated acid and one of water). The 

 residue was digested in water, and a plate of zinc immersed in 

 the filtered solution, caused the precipitation of the same quan- 

 tity of copper as in the previous process. Hence 100 parts of 

 this ore contain 



Copper 76.50 



Iron 0.50 



Sulphur 22.00 



Loss 100 



ibo 



Art. VI, Description of the Balance represented in 

 Plate V. fig. 1. 



A GOOD pair of scales is an essential implement to the 

 chemist and mineralogist, but it has hitherto been scarcely- 

 attainable, except at a price far too considerable for the gene- 

 rality of purchasers. We are indebted to our friend Mr. 

 Children for the drawing of the beam represented in the above- 

 mentioned plate, and which will, we believe, be found to possess 

 considerable accuracy in a small and convenient compass, and 

 at a very moderate expense. 



The beam, which is of platinum and made so light as to be 

 extremely sensible, is at the same time rendered sufficiently 

 strong by its form. The adjustments for bringing the points of 

 suspension of the scale pans, equidistant from, and in a right 

 line with the axis, are performed by the screws a and b at the 

 ends of the beam ; these screws also serve to strengthen the 

 curyed ends of the beam and prevent their bending. The 

 axis of the beam is a piece of very hard steel, of an equilateral 

 triangular form, passing through the beam and bearing on agate 

 planes; the knife edges are ground to an angle of 120°, which has 

 been chosen thus obtuse from the liability of a more acute edge 

 to be broken when suddenly lowered upon the agates. The 

 ends of the axis are chamfered from the top to the knife edge, 

 so that when the beam is lowered upon its bearings, they are 

 clear of the lifting frame. An index or pointer descends from 



