August 2 2, 1878] 



NATURE 



441 



cent, be dissolved in the water, the behaviour of the clay is quite 

 different. The larger particles soon subside, but the smaller 

 ones remain diffused through the liquid for a long time, giving 

 it a milky appearance, quite different from the flocky and grainy 

 appearance of the common water ; if i per cent, of sodium 

 carbonate be dissolved in common water, and china clay be 

 mixed therewith, the subsidence of the clay is still more rapid, 

 owing, as I have explained, to the increase in the electric con- 

 ductivity of the fluid, and the consequent decrease of pedesis. 

 But I now find that if soap be added at the same time, pedesis 

 is not destroyed but considerably increased, and the clay remains 

 a long time in suspension, two or three days at least. 



These facts give a complete explanation of the detergent 

 power of soap. It has long seemed to me unaccountable that 

 for cleansing purposes the comparatively neutral soap should be 

 better than the alkaline carbonate by itself ; we are told that the 

 alkali is but feebly combmed with the stearic or other fatty 

 acids. But why combine it at all if we need only the alkaline 

 power of the base ? The fact is that the detergent action of soap 

 is due to pedesis, by which minute particles are loosened and 

 diffused through the water so as to be readily carried off. Pure 

 rain or distilled water has a high cleansing power, because it 

 produces pedesis in a high degree. The hardness of impure 

 water arises from the vast decrease of pedesis due to the salts in 

 solution. Hence the inferior cleansing power of such water. 

 If alkaline salts be added, dissolved in water, it becomes capable 

 of actin;^ upon oleaginous matter, but the pedetic power is 

 lessened, not increased. But if soap be added also, we have 

 the advantage both of the alkali dissolving power, and of the 

 pedetic cleansing power. At the same time we have a clear 

 explanation why silicate of soda is now largely used in making 

 soap ; for I have shown, in the paper referred to, that silicated soda 

 is one of the few universal substances which increase the pedetic 

 and suspensive power of water. 



I believe that the detergent power of soap and water is one of 

 the many important phenomena which may be explained by the 

 study of pede-is, and I propose to follow up the investigation of 

 this movement in regard to .the several substances which tend to 

 increase it. 



Motions produced by Dilute Acids on some Amalgam Surfaces, 

 by Robert Sabine. — The author finds, when a drop of very dilute 

 acid is placed upon the clean and newly filtered surface of a rather 

 rich amal^fam of some metal which is positive to mercury, that 

 the drop does not lie stlil as it would do upon pure mercury, but 

 sets itself into an irre^jular jerky, motion. This is the case with 

 copper, zinc, antimony, tin, and lead amalgams. But if instead 

 of these amalgams those of platinum, gold, and silver are used — 

 these latter metals being negative to mercury — the drop of acid, 

 water lies quite still. The acids tried, were sulphuric, hydro- 

 chloric, oxalic, and acetic, which behaved similarly but in dif- 

 ferent de^ees. When. the experiment is made in an atmosphere 

 of oxygen the movenents upon the amalgams of the positive 

 metals are increased ; but in hydrojjen, carbonic acid, nitrogen, 

 and coal-^as the motions are instantly arrested. 



The author concludes that the motions result from an alternate 

 play of deoxidation of the mercury underneath the acid by elec 

 trolysis, due to the currents of small floating particles of the 

 positive metal causing the drop to contract, and of oxidation of 

 the surface outside the acid:drop causing it to re expand. 



On Certain Phenomena accompanying Rainbows, by Prof. 

 Silvamis P. 'iliompson. — The author narrated several instances 

 of rainbows seen chief^ in Switzerland, where radial streaks of 

 light devoid of colour were observed within the primary and 

 without the secondary bow. The explanation suggested'was as 

 follows : — T^>e wedge-shaped radial streaks are beams of sun- 

 light, which become visible by diffuse reflection from particles of 

 matter in their path, just as the apparently divergent beams of 

 sunrise or sunset become vi-ible. These "beams" being prac- 

 tically parallel to one another, appear to converge in the point 

 exactly opposite to the sun by perspective, or, in fact, ju-t as 

 the parallel beams of sunset appear divergent. Since the rain- 

 bow has for its centre the point opposite the sun, such beams 

 must have positions radial with respect to the bow. They re- 

 semble, therefore, the rayons du crSpuscule occasionally seen in 

 the ea^t at sunset ; they had never been observed crossing the 

 dark span between the primary and secondary bows. A similar 

 phenomenon of rays might sometimes be seen in sunli:(ht, when 

 the shadow of the observer fell upon a slightly turbid lake or 

 river. 



SECTION B. 



'chemical science^ 



Opening Address by the President, Prof, Maxwell 

 Simpson, M.D., F.R.S. 



My position here is a highly honourable, but by no means a 

 comfortable one. Naturally you expect to hear from me some- 

 thing new about the science which occupies the attention of this 

 section, and I have the miserable feeling that I must disappoint 

 you. How can I possibly find a fact in chemistry with which 

 you are not already acquainted ? If, in order to cater for you, 

 I go to France, Germany, Russia, or America, I find the 

 abstractors of the Chemical Society have been there before me, 

 and have swept everything of value into their journal. Chemists 

 are now kept perfectly acquainted with the progress of science 

 in every part of the world, and therefore the raiwn d'iire of 

 this address, so far- as announcing the discoveries of the year is 

 concerned, has passed away. I therefore propose instead of 

 giviu'.i' you a concentrated essence of the last twelve nuflibers of 

 the J<urnal of the Chemical Society, to bring before you the 

 clai;ns of this science to a place in general education, and the 

 claims of original research to a place in the curriculum for 

 higher degrees in our universities. 



I have been devoted to chemistry all my life. It has been 

 my business and my pleasure. The longer I live the more 

 deeply am I impressed with the advantages to be derived from 

 its study, and Iv am anxious that these advantages should be 

 shared by the rising generation. 



Whether we take into account the value of the knowledge- 

 acquired, the discipline of the intellectual faculties in acquiring 

 that knowled/e, or the effect on the character, surely we have a 

 right to give the study of this science a prominent place in our 

 schools and colleges. It would be difficult to over-estimate the 

 value and extent of the knowledge we derive from chemistry. 

 Without it we can Know nothing about the air we breathe, the 

 water we drink, or the food we eat ; we cannot understand the 

 processes of combu tion, respirationj fermentation, putrefaction,, 

 or the endless chemical changes which are continually in ope- 

 ration around us, n w ich affect our lives for good or for evih 

 In a word, the w hole of the phenomena of nature must for 

 ever remain to us, more or less, an inscrutable mystery. 



Again, is it not desirable that we should have some acquaint 

 ance^with the chemical arts, from which we derive so many of 

 our comforts and luxuries? Should we not know something of 

 the arts of photography, dyeing, metallurgy — something of the 

 manufacture of glass and china, and of the thousand beautiful 

 things that are constantly in our hands? Not only is the know- 

 ledge we obtain from chemistry very considerable in itself, bnt 

 it furni-hes us with a key which enables us to unlock vast stores, 

 of knowledge contained in several other sciences — these are, 

 physics, geolagy, mineralogy, physiology, and I may now 

 add, astronomy. Physics and chemistry are so intimately 

 connected that it is difficult to say where the one begins and the 

 other ends. The help that chemi try gives to physics is shown 

 by the numbers of chemists who have distinguished them=elves 

 as phy.'icists. I may mention a few belonging to our own time — 

 Andrew-, Bunsen, Faraday, Frankland, Graham, Guthrie, and- 

 Regnault. 



With regard to mental discipline, the mind of the student is 

 exercLed in both the inductive and deductive methods of reason- 

 ing. His original faculties are stimulated by the con ciousness 

 that he can in many cases readily test the worth of his ideas bjr. 

 experiment. With inexpensive apparatus and a good balance,^ 

 the intelligent student can make out for him elf some of the 

 laws and many of the facts of the science, and it may be, also 

 add^ to them. He glides insensibly from the known to the 

 unknown. Indeed his spirit of inquiry demand--, in most cases, 

 to be curbed rather than spurred. Some students are constantly 

 finding out new methods of analysis or discovering the precious 

 melah in impossible places. 



The readiness with which we can cross over into the terra 

 incognita of chemistry and make little explorations there, con- 

 stitute-, in my opinion, the great charm of this science, and, to 

 a great extent, its value as an educational a.gent. What I wish 

 to'^ini t upon is that the student of chemi try can reach the 

 field of original work sooner than the student of most other 

 ^ciences. Once he commences original research the develop- 

 ment of his intellectual faculties rapidly progresses. His 

 imi/ination is daily exercised in propounding ncvv theories 

 and devising experiments ip order to, ascerlaui their truth or 



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