72 SEC. 3. MEASUREMENT. 



In the steel capsule there is on the upper part, in the lid on the lower part, 

 an air-tight fitting cut in cock. The reservoir communicates with these 

 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 

 convenierft filling and emptying of 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 millims, 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. 



As auxiliary apparatus are furthermore required : 



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

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



2. A fine pair of scales indicating as much as 0*001 grammes, with a 

 bearing 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 pointed steel sole, and a sledge for 

 exactly measuring the difference in the level of the mercury menisci in the 

 two tubes 1 and 2. 



Theory of the Densimeter. 



Let the weight of the reservoir be, 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 evacuated, and filled with mercury, 

 let the weight of the same be, at t temperature of the chemically pure 

 mercury =T grammes. 



Consequently the contents of the reservoir filled bythe mercury amount to 



m T> 



I cub. centim. 



"13-59(1 -0-00018*) 



If now P grammes powder be filled into the reservoir, and the latter ex- 

 hausted of air, and thereupon filled again with mercury, the same will weigh, 

 at & temperature, only T 1 grammes consequently amounts the volumen of 

 the P. grammes powder, at t temperature, 



T-T' + P 



13-59 (1-0-00018 <) ' 



consequently the specific weight of the powder to be examined 

 ^specific weight^P 18 - 59 ^ ^'^'- 



The following examples will serve as illustration : 



The specific weight of chemically pure mercury amounts at 



Cels. = 13-59; 10 Cels.= 13'5" 19 Cels.= 13'55 ; 27 Cels. 

 r> Cels.= 13-58 ; .15 Cels. = 13'56 23 Cels.=J3'54. 



