90 SEC. 3. MEASUREMENT. 



cocks by means of two channels, which, for fine-grained powder, are shut off 

 by a steel tinplate filter, the holes of which.have a width of 0'3 mm. The two 

 tubes, 1 and 2, are screwed air-tight on the plugs of the two cocks 1 and 2. 

 At the upper ends of both tubes funnels of glass are squeezed in for more 

 conveniently filling and emptying the mercury. The shorter tube, No. 1, of 

 about 600 mm. length, carries in the centre a glass-tube, about 200 mm. long, 

 divided into niillims, and can, just above this tube, be closed air-tight by 

 means of a screw cramp. The interior diameter of the tube No. I is about 

 9 mm., whilst that of tube No. 2, which is about 2,500 mm. long, measures 

 only about 5 mm. The gutta-percha tubes are spun over on the outside. 



Reservoir and tube 1 are fastened in a wooden frame ; funnel 2 is in a 

 wooden- lining. 



This precaution has been taken for the reason that the temperature of the 

 mercury and of the apparatus should be altered as little as possible during the 

 operation by the warmth of the hands. By means of two strings, which run 

 over rollers fastened in the ceiling of the room, funnel 1 and funnel 2 can be 

 pulled up or down at pleasure. 



The auxiliary apparatus further required : 



1. A thermometer, by means of which, previous to, during, and after the 

 filling in of the mercury, the temperature of the same will be ascertained. 



2. A fine pair of scales indicating to 0*001 grammes, with a carrying 

 capacity of 6 kilos, (each scale 3 kilos.) 



3. A barometer for determining the pressure of the atmosphere at the 

 place of operation. 



4. A wooden scale, 1 m. long, with a steel point, and a slide for exactly 

 measuring the difference in the levels of the mercury meniscus in the two 

 tubes 1 and 2. 



Theory of the Densimeter. 



Let the weight of the reservoir, with the tubes screwed off, but inclusive 

 of the connecting piece screwing the capsule and the lid together, = R 

 grammes. After the reservoir has been exhausted, and filled with mercury, 

 let its weight at temperature t of the chemically pure mercury =T grammes. 



Consequently the contents of the reservoir filled bythe mercury amount to 



rp *D 



cub. centim. 



13-59(1 -0-00018 fr 



If now P grammes of powder be placed in the reservoir, and the air exhausted 

 and the remaining space filled with mercury, the whole will weigh, at 

 temperature t, only T' grammes, hence if Y is the volume of the P grammes 

 powder, at t temperature, 



T-T' + P 



13-59 (1-0-00018 <) 

 consequently the specific gravity of the powder to be examined 

 * =spec ifi c g*y-r"*(*_-^"q- 



The following examples will serve as illustration : 



The specific gravity of chemically pure mercury amounts at 



Gels. = 13-59; 10 Cels.= 13'5 n 19 Gels. = 13-55 ; 27 Cels.= 13'53 

 5Cels.= 13-58 ; 15 Cels. = 13'56 23 Cels. = 13'54. 



