92 SEC. 3. MEASUREMENT. 



The extension of the examples 1 and 2, therefore, is essentially facilitated : 



Example 1. 



Given P= 60 gr. t= 19 C., consequently 13-59 (1 19 0-0318) = 13'53 



T=1091-6 grammes, T' = 61 1-6 grammes. 



Example 2. 



Given P = 42 grammes <=190 C., 



consequently specific weight of mercury =13*55. 

 T= 1091-6 T'= 808-4 



Because the expansion coefficient of the reservoir made of steel is different 

 for changing temperatures from that of the mercury, it will be necessary for 

 determining once for all empirically the weights of Tn for +0, +5, 10, 15, 

 20, 25, 30, 35 Gels., to calculate the required cubical contents of the reser- 

 voir = Vn, to interpolate them graphically, and to embody them from degree 

 to degree in a table. 



DIRECTIONS FOR USE OF THE DENSIMETER. 



The temperature of the mercury is determined and noted before, after, and 

 during the period of operation. For that purpose it is advisable to employ a 

 thermometer composed of a very fine glass tube, which admits of being 

 inserted in the gutta-percha tube No. 1, which has been filled up to the 

 aperture of the funnel. 



The mercury in funnel 1 will show, on account of the friction and con- 

 sequent heating, 13 more heat than that in funnel 2. This difference is, 

 however, equalised in a very short time. 



During the operation the apparatus must only be touched on the wooden lining, 

 in order to avoid as much as possible any variations in the temperature which 

 may be caused by the warmth of the hands. The powder to be tested must 

 be of nearly the same temperature as the mercury to be employed, for which 

 purpose it will be best to keep both before the testing operation for several 

 hours in the same room. The reading of the barometer which indicates the 

 pressure of the atmospheric air must be noted down. 



The two tubes 1 and 2 are screwed air-tight to the reservoir, the two cocks 

 are opened, and the apparatus fastened in the wooden frame with vertical 

 position of the tube No. 1. 



Thereupon the funnel T" is lifted to the level of T' (upon +760 mm.), and 

 chemically pure mercury poured into the funnel T", until both funnels are 

 filled with mercury to a height of about 20 mm. The mercury will then stand 

 760mm. high above the ( + 0) point of the reservoir; consequently the 

 pressure upon the highest point of the reservoir will be altogether two atmo- 

 spheres (1 atmosph. pressure corresponding in the mean to 7-fi.O mm. mercury. 



Under this pressure the air in the reservoir will for the greatest part be 

 already forced up, and in fact in the direction towards funnel 1. 



Now the cramp screw-piece is attached below the funnel 1, and above the 

 glass tube in the centre of the hose 1 filled with mercury, and the latter shut off 



