December i, 1892] 



NATURE 



obtained by measurements of other properties of salt 

 solutions, the electric conductivity, the depression of 

 the freezing point, &c., and the theory is compared with 

 practice by seeing if the values of " /," as determined, say, 

 from freezing point observations, agree with those de- 

 duced from the osmotic pressure. The comparison shows 

 that in some cases, some half-a-dozen in all, the two sets 

 of values correspond ; in others, and in by far the majority, 

 no such correspondences exist. In these latter instances 

 it is argued, and with a certain amount of experimental 

 evidence, that the salts were not without action on the 

 membrane employed, and that, therefore, diosmose 

 really took place, the membrane was not truly semi- 

 permeable. In this way the discordant observations 

 have been put out of court. 



It is thus apparent that the leading hypotheses of the 

 new theory do not receive confirmation of the weightiest 

 kind from observations on osmotic pressure. Indeed, 

 were they supported by such measurements alone, they 

 would hardly be entertained. Their mainstay, however, 

 ies in the mass of experimental work on many other 

 properties — evidence which it is much easier to obtain 

 than the difficult measurements on osmotic pressure — 

 which has been correlated and explained by their use. 



been put forward in favour of the gaseous analogy. 

 Several physicists, starting from entirely different points 

 of view, have arrived at the result that in a dilute solu- 

 tion the dissolved substance should obey laws similar to 

 those which hold for gases. At present the attitude of the 

 prominent upholders of the new theory is one of indif- 

 ference as to the exact mechanism of osmotic pressure. 

 The numerical agreement between the measurements on 

 solutions and those on gases is regarded as ample justi- 

 fication for considering dissolved substances to be in a 

 pseudo-gdA&ow?, condition. 



Whatever the ultimate explanation of the facts may be, 

 there can be no doubt that the existing speculations on 

 the nature of osmotic pressure and allied phenomena 

 have infused new life into the study of solutions. Indeed, 

 as instigators to fresh inquiry these hypotheses must 

 take rank as the most fruitful of recent times. 



J. W. Rodger. 



A SANITARIAN'S TRAVELS. 

 TV/TR. ROBERT BOYLE has travelled round the world 

 ^^^ no fewer than four times for the purpose of study- 

 ing sanitary science and preparing the way for the intro- 



GREAT RECUMBENT FIGURE OF BUDDHA, PEGU. BURMAH. 



It is only fair to add that both hypotheses, from physi- 

 cal as well as chemical standpoints, have met with a 

 measure of adverse criticism. The role played by the 

 membrane has also been questioned. It has been sug- 

 gested that it is not really semi-permeable, allowing sol- 

 vent only to pass, but just as a porous plug behaves 

 towards a mixture of gases, it allows molecules with dif- 

 ferent momenta to traverse it at different rates. Or, 

 again, its action has been likened to that of a palla- 

 dium film towards hydrogen, compounds being formed 

 with the membrane substance on one side, these becom- 

 ing diff"used and dissociated on the other. If either of 

 these views be correct the pressures exerted by dissolved 

 substances have probably never been measured. 



On the other hand, important theoretical support has 



NO. 1205, VOL. 47] 



duction of the ventilating and sanitary appliances he has- 

 invented. An interesting account of hisfourlii j j'uney is 

 given in a little book entitled "A Sanitary Crusa.ie 

 through the East and Australasia," consisting of a series 

 of papers reprinted from the Building News. In the 

 course of this "crusade" Mr. Boyle visited Burmah, the 

 Malay native states, Sumatra, Siam, Borneo, Java, Aus- 

 tralia, New Zealand, Samoa, the Sandwich Islands, and 

 America. Of all the facts noted by him as a sanitariaiv 

 the most remarkable are those relating to leprosy, a dis- 

 ease which he believes to be spreading to an alarming 

 extent all over the world. He was particularly struck by 

 the gigantic proportions the evil has assumed in Burmah. 

 The steps of the great Shwedagon pagoda at Rangoon, 

 the Mecca of the Indo-Chinese Buddhists, he found to be 



