264 Neio Instrument for Specific Gravities. 



something new in the mode of applying it. The only method hitli- 

 erto resorted to in taking the sp. gr* of minerals is to compare the 

 actual weight of the mineral in air with the loss of weight it sustains 

 in water. The mode adopted here is to compare the actual weight 

 of the mineral with the weight of water displaced by its immersion. 

 The theory appears to me unobjectionablej but I anticipate difficul- 

 ties in bringing the instrument into correct operation, although none 

 but what a skilful artist might overcome. 



Construction. ' 



A cylludrical tube 0.13 of an inch iu diameter will hold by 

 calculation a trifle more than 30^ grains of distilled water. Pro- 

 vide a glass tube of these, or nearly these dimensions and the same 

 ■ in quality as those used for the best barometers. Let one end of the 

 tube (b) be supplied with a top (a) to screw on and off and to be per- 

 fectly water tight when on. Let the other end of the tube (c) be 

 luted into a low round glass bottle about half an inch in diameter and 

 the same in height, the upper half of which is to be funnel shaped 

 and made, by means of a metal joint, to screw on and off the lower 

 half, but like the top (a), to be perfectly water tight when on. This 

 bottle is marked (tZ, e^fg, h^ i,) iu the accompanying sketch and the 

 position of the screw is shewn by the dotted line (e, A.) The tube, 

 thus prepared, is fixed to a board such as is used for thermometers 

 and in die same manner with die exception that the botUe projects 

 beyond the lower end of the board. 



Carefully weigh in a delicate pair of scales turning with a tenth of 

 a grain, 30 grains of distilled water at the temperature of 60^ of 

 Fah. which pour into the tube (6c) by the funnel {d, e, h, 

 observe the height at which this water stands in the tube in its pres- 

 ent reversed position and score the same on the board. Divide this 

 height into as many equal parts as there are tenths of grains in the 

 water and score these also on the board commencing with 5 or 10 

 near the bottom and terminating at 300 at the top — -every one of 

 these divisions will of course represent a tenth of a grain which 

 mark as in the sketch. 



JSIanner of using the instrument. 



Turn the top [a) downwards and unscrewing the cylindrical por- 

 tion of die botde {efg h) fill the tube with water by tlie funnel {deh i) 

 and observe the height at which the water stands, then screw on the 

 part {efg h) and allow the water to fall tlirough the tube into the botde 



