On Steam and Brines \ 59 



sound. Tenths of a Centigrade degree are then uncertain. 

 Yet it is essential that there should be an abundant flow of 

 steam through the tube; therefore, the exit tube must be 

 sufficiently wide to allow the steam to issue in a stream of 

 good volume, and must not be so wide as to incur any risk 

 of regurgitation of air. Again, the entry tube for the steam 

 must not be too narrow. It is not essential, but it is very 

 convenient, that it should be so wide that the steam condensed 

 on the walls and flowing back into the boiler should continue 

 to flow down the sides of the entry tube and not collect at 

 the bottom of the wide part of the tube. When the steam 

 proceeds along a short straight passage from the boiler to 

 the steam tube, it throws about any water in a violent and in- 

 convenient way. In a tube which I use for this purpose the 

 entrance tube has a diameter of 9 mm. and the exit tube 

 10 mm. The entry tube is thus wide enough to permit the 

 condensed steam to flow back along its sides ; at the same 

 time, it is smaller than the exit tube, so that, apart from the 

 continual condensation of a portion of the steam, there is no 

 danger of the tube receiving more steam than it can freely 

 get rid of. 



That an apparatus such as that here described does, in 

 fact, exclude the possibility of the steam supplied having a 

 tension which differs at all from the pressure of the atmo- 

 sphere with which it exhausts, will be evident from the 

 following experiments. The small copper flask, the spirit 

 lamp, and the steam tubes above described were used. The 

 thermometer was divided into fiftieths of a degree Centigrade, 

 the length of one degree being 35 mm. The atmospheric 

 pressure happened to be pretty high, and when the thermo- 

 meter had taken the temperature of the steam the top of the 

 mercury was exactly even with the centre of the line on the 

 scale marking ioo'i8 C. It occupied this position when 

 steam was being generated at its highest rate of 8-4 grammes 

 per minute. The flame of the lamp was reduced by degrees 

 until it reached its lowest point, when steam was being gene- 

 rated at the rate of 2*4 grammes per minute. It was then 

 issuing continuously, that is, there was no regurgitation, but 



