28 Transactions of the Royal Canadian Institute 



tilation (associated with the names of C. E. A. Wins low, D.D. Kimball, 

 G. T. Palmer, F. S. Lee, J. A. Miller and others), and also of the Chicago 

 Department of Health (under the direction of Dr. E. Vernon Hill), 

 have appeared in numerous articles published by the American Journal 

 of Public Health, the Journal of the American Society of Heating and 

 Ventilating Engineers, the Journal of Industrial and Engineering 

 Chemistry, Domestic Engineering, the American Journal of the Medical 

 Sciences, the American Journal of Physiology and others. Some of 

 these papers present an amount of elaborate investigation which should 

 be reviewed most carefully by any prospective investigator. Further 

 references are given at the end of this article. 



As the purpose of this article is to interest and to attract more workers 

 to a fertile field, a list of a few of the simpler problems pressing for atten- 

 tion is submitted below, together with the practical spur of some sug- 

 gestions of procedure for several of them. 



Problems 



(1) The variation of vapour pressure with temperature for all 



the characteristic hygroscopic substances should be thoroughly 

 investigated. These data would be of great value in the develop- 

 ment of several types of hygrometers, in the study of evaporation 



^ from skins and plant surfaces, and in the determinations of the mois- 

 ture content of certain materials. 



It is suggested that thin specimens of a given hygroscopic 

 substance be prepared with a very large sur ace per unit volume. 

 A calibration should then be made of several of them for changes in 

 weight under the influence of varying external vapour pressure, — 

 care being taken that the temperature of the substance is the same 

 as that of the surrounding air, whenever a weight is recorded. 

 This calibration can be made conveniently by suspending the 

 specimen successively in a series of closed jars each of which contain 

 at the bottom a diluted deliquescent salt of previously ascertained 

 vapour pressure. The weight can be obtained with a delicate 

 balance when equilibrium is reached, by means of a wire passing 

 through a suitable long tubular hole in the top of the jar, which 

 should be sealed between readings. 



One of these specimens will then constitute an accurate cali- 

 brated hygrometer which will exhibit the same phenomena and the 

 same peculiarities as the material to be examined. If it is then 

 suspended in a jar which is kept at a constant temperature, and 

 connected by a tube to another jar containing a similar specimen, 

 it should be possible by varying the temperature of a bath round 



