THE REGULATION OF TEMPERATURE. 71 



of Type III, the interior portion of the system has been replaced by a 

 single large pipe of ring form, which is so arranged on the inside that the 

 hot water is returned to the upper part, while the colder water is con- 

 stantly pumped out of the bottom. 



The motor fan (9) is employed to keep the air in the inclosed space in 

 circulation over the heated pipes and over the lamps; but it serves also 

 to keep the manometers gently but constantly agitated, and thus to 

 overcome the tendency of the mercury to lag in the tubes. This agita- 

 tion is increased to any desired extent by attaching bits of stiff paper 

 to the upper ends of the manometers. 



The external appearance of the bath is seen in Plates 4 and 5. 

 In the latter, the system of pipes for the circulation of hydrant water, 

 which should be seen at the top of the interior, has been removed, as 

 this bath is but little used for temperatures below that of the air. 



The other baths of the same general type (two in number) were 

 planned with reference to the measurement of osmotic pressure at low 

 or very moderate temperatures. They differ from the bath described 

 mainly in the care which has been taken to protect the interior from 

 external temperature conditions. Their wooden walls are all double 

 and the intervening space is filled with hair. Moreover, the small 

 rooms in which they are located are made subject to temperature regu- 

 lation by means of pipes covering the ceiling through which hydrant 

 water is circulated when necessary. A further means of cooling these 

 bath rooms consists of a chute opening upon the outside of the building, 

 through which air is introduced into the room at any desired rate by 

 means of a rotary fan. Formerly it was attempted — by means of a cir- 

 culating system for hydrant water, by the introduction of a regulated 

 quantity of air from the outside, and by means of gas stoves under the 

 control of thermostats — to keep the bath room as nearly as possible at 

 the temperature of the bath; but with the present improved facilities 

 for the internal regulation of the baths, this is no longer necessary. The 

 recent practice is, in general, to keep the temperature of the room 4° or 

 5° below that which is to be maintained in the bath. The flexibility of 

 the system of temperature regulation, however, is such that differences 

 of temperature amounting to 25° can be easily tolerated. At the highest 

 temperatures at which osmotic pressures have been measured, differ- 

 ences of 60° were not infrequent. 



Type IV. 



The baths previously described, which are made partly of wood, are 

 not adapted to the measurement of osmotic pressure at high temper- 

 atures. For this purpose, it was necessary to construct baths of differ- 

 ent design and wholly of metals. 



The baths for high temperatures, which are equally well adapted to 

 work at low temperatures, are of two sizes and are made of heavy 

 sheet brass and copper — mainly of the former. A (Figure 38) exhibits a 



