STEAM AND BRINES. 543 



numbers. The experiments are numbered consecutively in the first headline (N), while 

 under n each line in the table is numbered consecutively from upwards. In this way 

 any entry in the table can be referred to at once by its co-ordinates (N, n). The second 

 headline gives the name and quantity of salt taken expressed in gramme-molecules. In 

 the third headline will be found the temperature of saturated steam, or that of pure 

 water boiling at the same time and place. The temperature of the boiling mixture or 

 brine is obtained at once from the values of T and (t — T). 



The figure is always used as a suffix when the boiling mixture of steam and salt 

 or saturated brine is being dealt with. Thus t , p , W always represent the tempera- 

 ture of the boiling saturated mixture, the steam tension of pure water of that tempera- 

 ture and the dilution of the mixture ; that is, the weight of water exactly saturated by 

 the amount of salt at temperature t . The temperature of the mixture when the steam 

 was stopped for the first time, and the first weight of condensed steam, W 1; ascertained, 

 is always t v It has already been pointed out that it was the custom to stop the steam 

 while there were still some particles of solid salt present, and while the temperature of 

 the mixture showed that there was also already unsaturated water present. The idea 

 was that the moment might be correctly judged when the amount of free salt present 

 would be just enough to saturate the amount of free water if time were given. As a 

 matter of fact, this was in most cases very nearly attained, as will be seen by comparing 

 the observed values of Wj with the computed values of W 2 in the cases where t Q — t x is not 

 more than 0*1° to 0*3° C. When this difference is larger, then the passage of steam has 

 not been interrupted until all the salt has disappeared. This is the preferable practice. 

 When any solid salt is present, and the temperature has fallen below the maximum, we 

 know exactly the temperature of the boiling brine and the weight of water in it, but as 

 there is an uncertain proportion of the salt originally taken which has not passed into 

 solution, the concentration or dilution of the brine is uncertain. For this reason it has 

 been impossible in the majority of cases to use t x and W x in the computation of W . 

 The values of W have been arrived at in the following way : — The difference 

 W 2 (£ — T) 2 — W s (t — T) 3 is found, also the differences t 2 — 1 3 and t — t 2 , then we as- 

 sume that 



W («-T) =f^ 2 {W 2 (*-T) 2 -W 3 (#-T) 3 }+W^-T) 2 



h ~ h 



and this value divided by (t — T) gives W . Thus in experiment No. 1 on 0*2 KG, 

 when T= 100-44° C, we have W 2 (*-T) 2 = 217*6, and W z (t-T) s = 212*9, their differ- 

 ence being 4*7. Also t — t 2 = 0-81° C, and t. 2 -t s = 1*05°, whence we have 



W o 0-T) o =^4-7+217-6 = 22O-6 



whence W = 26-30. 



It will be seen that the value of W x is 25*91, and < 1 -T = 8 , 28°, only 0*11° C. below 

 £ — T. The passage of steam had therefore been stopped too soon ; there was solid 



