222 



Mr. R. F. D'Arcy on the 



H 2 S0 4 . H 2 0. As more water is added the viscosity decreases 

 continuously. All Graham's experiments were made at a 

 temperature of 20° C. 



In the following experiments, by working at different tem- 

 peratures, it is found that this increase of viscosity on the 

 addition of water occurs at temperatures below about 65° C. : 

 at higher temperatures the viscosity diminishes continuously 

 as the concentration diminishes. 



The apparatus used was very simple. It consisted of a 

 bulb, A, which was connected by the tube, B, with a gas-bag 



to gas-bag and 

 pressure-gauge. 



containing air under pressure, and to a water pressure-gauge, 

 and by C to the fine tube, D. The capacity of the bulb A 

 between the two scratches a and b is 15*9 c.c. 



The experiments consisted in observing, by means of a 

 stop-watch, the time taken to empty the bulb A of the liquid 

 under examination through the tube D, the pressure being 

 measured by means of the water-gauge, and the temperature 

 by the thermometer, T. The water surrounding the bulb A 

 and the tube D was kept at a uniform temperature by means 

 of the stirrer, K. 



No great accuracy was aimed at in these experiments ; the 

 object being to establish in a general manner the alteration of 

 the relation of viscosity to concentration at different tempera- 

 tures, rather than the accurate determination of the viscosity 

 of the different solutions used. 



The acid used contained 2 per cent, of water. It was free 

 from lead. Four solutions were used in addition to the undi- 



