SPECIFIC GEAVITY OF LIQUIDS. 41 



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sp. gr. of the mineral JQ- = 2'7. Instead of weigh- 

 ing the displaced water, it may be measured in a gra- 

 duated vessel. Thus if it is found that a piece of brass 

 which weighs 160 gr has displaced 20 CC of water, the 



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sp. gr. of the brass will be - =8, for 20 CC of water 



weigh 20 gr . 



A somewhat large tumbler, having a hole bored near the upper 

 edge, may serve for the last experiment. The hole is bored with a 

 round file, of which the point is broken off, so that a round surface 

 of from 2 to 3 mm in diameter is obtained. The edge of this round 

 surface is used for drilling, the file being held with the right hand 

 in a slanting direction, and the thumb being kept quite close to 

 the broken end of the file, in order to increase the pressure and 

 also to prevent the file from slipping through the finished hole 

 and breaking the glass. File and glass must, during the operation, 

 be frequently^ wetted with water or, better still, with oil of tur- 

 pentine. After piercing the glass completely by the point, the 

 hole is enlarged by slowly turning the file from right to left, in 

 the manner in which a screw is drawn, repeatedly moistening the 

 orifice and the file. If a wider orifice is required than the thickest 

 part of the file, the latter is used simply for widening it by filing 

 equally all round, care being taken not to make the aperture 

 angular by working too long at any point. It is advisable to 

 practise the operation first on a few pieces of broken glass. A 

 small piece of bent tubing is now inserted into the vessel by means 

 of a short india-rubber tube, half of which is first passed into the 

 aperture, into which it must fit tightly, the greased glass tube 

 being then cautiously pushed with a turning motion into the 

 india-rubber tube. The end of the bent tube must be rounded before 

 the lamp. 



The specific gravity of a liquid is found by weighing 

 a little flask provided with a well-ground stopper, first 

 filled with water and afterwards with the liquid. Care 

 being taken that at each weighing the flask be completely 

 filled with the liquids, the weights of equal volumes of 



