128 ROCHESTER ACADEMY OF SCIENCE. [April l8, 



larger than that of the inner tube and smaller than that of the outer 

 one. The proper thickness of wire to produce the best results may 

 be determined by e.xperiment within the limits fixed by the above 

 condition. 



The fulfillment of conditions / and ^f rests with the operator. 



//. Manipulation of the Apparatus. 



We give below a somewhat detailed description of the mode of 

 operating our apparatus, because it often happens that, from inob- 

 servance of certain rules or ignorance of certain wrinkles, a new 

 contrivance is frequently put aside as worthless, that with more care- 

 ful tes?ting has given very good results. 



In operating the apparatus, the following order should be 

 observed : 



I. — The water regulator is prepared for the whole duration of 

 the operation by opening the cock to the supply tube a, fig. i. 



2. — After carefully joining together the different parts of the 

 apparatus, the cock a, fig. 3, is opened and water slowly admitted 

 into the separator. It is important that no air bubbles are allowed to 

 remain in the connecting tubes and that the water should rise to the 

 height of a few centimeters in the space /. The exclusion of bul> 

 bles may be easily effected by filling the space / from a wash-bottle 

 before joining the separator and regulator, and by filling in the same 

 manner the rubber tube by which these two parts are joined. 



3. — Before the liquid column reaches the point /, (fig. 2,) the 

 lateral tube h is closed with a rubber tube and screw-clip and the 

 whole apparatus is then filled up to the funnel /, when the cock^;, (fig. 

 3,) is again closed. 



4. — The mineral mixture is introduced through the funnel /. 

 The particles sink and lodge in the space ^. The size of the grains 

 must not be too great to move freely in this space so that in the case 

 of a coarse sand, a larger apparatus than the one here described may 

 be required. The amount to be operated upon at one time will 

 naturally depend upon the size of the space ^, which should not be 

 over a quarter full. In our experimental apparatus, we have oper- 

 ated upon about two grammes at a time. The apparatus will operate 

 equally well upon very much smaller amounts, and is continuous in its 

 action, since it is clear that, after the first portion is withdrawn, 

 another can be added without any derangement of the apparatus. 



