53G Mr. A. Griffiths on an Apparatus for the Determination 



the top taps will allow a sudden rush to take place up the 

 tubes. 



It is obvious that a diminution of temperature produces an 

 error in the opposite direction ; and the error produced by a 

 fluctuating temperature will probably not be considerable in 

 the long run. 



Section V. — Errors clue to Changes in Volume produced by 

 the Weakening of the Solution through Diffusion. 



In general, when a solution loses some of the dissolved sub- 

 stance by diffusion it diminishes in volume. The diminution 

 depends on the nature of the dissolved substance and varies 

 with the concentration. The diminution for any given loss 

 can be calculated from a table of densities. For example, an 

 aqueous solution of copper sulphate at a temperature of 23°*3 

 containing 80 grams to the litre has a density of 1*080, 

 whereas a solution containing 160 grams to the litre has a 

 density of 1*154. It can be readily shown that the addition 

 of 1 gram of anhydrous copper sulphate, between the given 

 limits, on the average increases the volume by 0*075 c.c. 

 approx. 



As in Section IV. it will be assumed that the upper com- 

 partment is open to the atmosphere. 



Since the diminution of volume of the lower compartment 

 equals the quantity of copper sulphate transmitted multiplied 

 by 0*075, with the aid of Sec. I. " Diffusive Convection/' it 

 can readily be seen that 



-0-075 xTxv 



u= = -^ 



1—e * 



Hence, neglecting the second and higher powers of —r , 



^ =0-075 xT. 

 k 



Let T=0*12, then ^=0*009. 



The fractional diminution in the quantity transmitted equals 

 vli/'2k, i.e. 0*0045. Thus the motion along the tubes causes 

 a diminution in the quantity transmitted by about one half 

 per cent. 



With salts whose solutions experience greater changes in 

 volume, the error may be very appreciable. 



Thus, between the limits of density 1*081 and 1*159, the 

 addition of 1 gram of sodium chloride causes an average 



