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ROCHESTER ACADEMY OF SCIENX'E. 



[April i8, 



■employed, the more complete should be the separation, because the 

 same lifting power could be obtained with a weaker current. Con- 

 trary to our expectations, we found that the difference between the 

 action of a current of water and one of the Thoulet solution is not 

 sufficient to make the employment of the latter advisable, and as any 

 advantage derived from a weakening of the force of the current is 

 more than compensated by the greater facility and economy of work- 

 ing with water. A repetition of the process with water will generally 

 be found more satisfactory than an attempt to obtain an equally good 

 separation with a single operation by the use of heavy liquids. 



In dealing with extremely heavy minerals, cases might arise in 

 which the use of heavy liquids would be of advantage, so that a 

 description of the apparatus fig. 5, employed in our experiments 

 will not be out of place. 



200 cu. cm. of liquid are sufficient for unin- 

 terrupted work. The other parts of the appara- 

 tus require no special alteration. The mode 

 of mounting and operating the regulator will 

 be understood without further description since 

 it has long been employed for water baths. 

 For convenience in filling the reservoir balloon, 

 two rather wide cocks, /i and /i' are employed. 

 From time to time the liquid that has run 

 through the apparatus is restored to the balloon 

 by opening the cock /i and closing /i'. After 

 pouring in the liquid, /i is again closed and //' 

 opened. These cocks require to be rather 

 wide (about 10 mm.) in order not to impede the 

 passage of air at // and of the liquid at //'. 



2. — The problem of regulating the current 

 is solved with sufficient accuracy by the arrange- 

 ment shown in figs, i, 3 and 4. Fig. i is the 

 pressure regulator kept at a constant level by 

 the overflow tube />. After opening the cock in connection with the 

 supply tube a, the regulator requires no further attention. The flow 

 is regulated by the cocks a and d, fig. 3. The first is for coarse 

 adjustment, rapid opening or closing, etc. The second, on the con- 

 trary is a " precision cook," whose special features (scale, counter- 

 poise and triangular valve) are seen in figs. 3 and 4. The necessary 

 sensibility of the cock is obtained through "a triangular opening 



