132 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Arrangement of the Apparatus as a whole. — Figure 5 shows how 

 these three pieces of apparatus are connected. It will be seen that the 

 viscosity apparatus and the transpiration apparatus are joined by the 

 glass tube L, and that a common tube leads from them to the pump by 

 way of a tube, M, containing granular silver, and one, N, containing 

 sulphur which has been fused and then powdered. The sulphur is in- 

 tended to prevent mercury vapor from passing from the parts of the 

 apparatus in which there is mercury to the other parts. The silver is to 

 absorb the sulphur vapor. As a means of testing the purity of the air 

 used, a spectrum tube, not shown in Figure 5, is inserted between the 

 tube containing silver and the main part of the apparatus. The figure 

 shows how the McLeod gauges are connected to the other parts of the 

 apparatus. The tube, P, leads to the pump. The connection between 

 the viscosity apparatus and the transpiration instrument is a long 

 spiral tube, so that the former may be rotated through a considerable 

 angle without disturbing the latter. 



The piece marked A' is for the purpose of admitting dry air or other 

 gases, and consists of about 2.5 m. of 2.5 cm. tubing containing phos- 

 phoric anhydride, and 1.25 m. containing chloride of calcium. The gas 

 is admitted through a tube, G, whose end passes under the flared out 

 end of the barometer tube, H. The bottle, I, contains mercury form- 

 ing a seal. The drying tubes may be connected to a bellows, if air 

 is to be experimented with, or to a gas generator. The gas rises in 

 bubbles through the mercury to the bulb, J. The small bent tube K 

 is to prevent the mercury from being driven through the apparatus 

 when a bubble of gas rises. 



The mercury pump has no stop-cocks. It has one mercury-sealed 

 valve. The auxiliary is a mechanical pump which can reduce the 

 pressure to two or three millimeters. 



The viscosity apparatus, the transpiration apparatus, and the gauges, 

 are placed on an iron support inside of an electric oven. The first and 

 second pieces are each placed in a double walled sheet iron box, whose 

 wall space is packed with asbestos. The fronts of these boxes are 

 removable, as is also the front of the oven. The purpose of the oven 

 is to provide means of heating the whole apparatus to a high tempera- 

 ture to insure drying and to free the inside of the glass from the 

 carbon dioxide which invariably adheres at ordinary temperatures and 

 pressures. 



When the different parts of the apparatus were set in position and 

 sealed together, and before the suspensions had been raised, or any 

 pumping had been done, the front of the oven was closed and heat 

 applied so as to maintain the temperature at 200° C. during a whole 



