386 APPENDIX. 



hardly necessary to state here that the interval of temperature 

 between the melting point of ice and the maximum condensing 

 temperature of saturated aqueous vapour at the normal pres- 

 sure, is divided in the Centigrade scale into 100 equal parts or 

 degrees, in the Fahrenheit scale into 180 degrees, and that the 

 scale commences from the melting point of ice in the former, 

 but from a point 32 below this temperature in the latter. 

 Hence the equations 



C. = | ( F.-32) 

 andF. fC. + 32. 



Though these formulae are simple enough and easily remem- 

 bered, when many conversions have to be made they are 

 troublesome. A graphical method of connecting the two has 

 been found very convenient in practice, and the diagram on 

 p. 385 will be useful, as it enables a temperature expressed 

 in either scale to be converted into the corresponding tempera- 

 ture in the other scale, without the trouble of interpolation. 

 The graduations extend from -35 C. (-31 F.) to 145 C. 

 (293 F.) commencing in the lower left-hand corner and 

 increasing in all cases as the stem is ascended. 



TABLE OF THE SOLUBILITIES OF VARIOUS SALTS IN WATER. 



The following table, giving the solubility of certain salts 

 used in agriculture, may be useful. One hundred parts by 

 weight of water at the temperatures stated dissolve the follow- 

 ing parts by weight of the various salts": 



At 10. At 100. 



Alum, ammonia, (NH 4 ) 2 SO 4 .A1. 2 (S0 4 ) 3 .24H 2 9-2 422-0 



,, potash, K 2 S0 4 .A1 2 (SO 4 ) 3 .24H 2 ... 9-5 357-5 



Ammonium chloride, NH 4 C1 ... ... 33-3 77'3 



sulphate, (NH 4 ) 2 .S0 4 ... 73*0 103-3 



Borax, Na 2 B 4 O 7 .10H 2 ... ... 4-6 201-4 



Boric acid, H.B0 8 ... ... ... 2-9 34-0 



Calcium carbonate, CaC0 3 ... about 0-0013 ? 

 , , (in water saturated with 



C0 2 at21) ... 0-099 



hydrate, CaH 2 O 2 ... ... 0-177 0-0766 



* Taken chiefly from Comey A Dictionary of .Solubilities, 1890. 



