APPENDIX. 383 



V = the required volume at standard temperature, o C., and 760 mm. Hg. 

 Y 1 = the volume at the observed temperature and pressure. 

 Ji = the observed pressure. 



= the coefficient of expansion, which is a constant (.003665). 

 = the observed temperature. 



The formula is obtained as follows : 



With reference to the correction of the given volume for temperature : 



i+at : I : : V 1 : V 



. 



i+at 

 and for pressure : 



.-.v= 



Example. Suppose the volume of gas to be corrected for temperature and 

 pressure, i.e., V 1 = 3O cc., the observed barometric pressure, i.e., ^ = 740 mm., 

 and the temperature of the room, i.e., 2= 15 C., then the required volume 

 will be : 



V- 30X740 = 22200 = ^ 



760 ( I +. 003665 x 15) 801.78100 



i.e., 30 cc. of a gas at 740 mm. pressure and 15 C. are reduced to 27.6 cc. at 

 standard pressure and temperature (760 mm. and o C.). 



SOLUBILITIES IN WATER AT 15 TO 18 C. 



Ammonium chloride 36 per 100. 



Sodium chloride, 3 



Ammonium sulphate, 5 



Magnesium sulphate, . . . . . . 125 



IV. 

 RECORDING APPARATUS. 



There are many forms of recording apparatus in use, and some of them are 

 described in the text (Lesson XXXIV.). When a number of students have to 

 be taught to record graphically the results obtained in an experiment, then 



