titntifn JUuns 



FOR GENERAL READERS. 



Vol. II. 



NOVEMBER 16, 1888. 



No. 20. 



Scientific Table Talk 



The Marine Zoological Station at 

 Algiers (/litis.) 



Roman Remains at Llantwit-Major 

 (Illus.) 



Prevision of Earthquakes 



General Notes ... ... 



On Vernation and the Methods of De- 

 velopment of Foliage, as Protective 

 against Radiation (Illus.) 



Water as a Constituent of Organic 

 Substances 



Natural History — 



Officinal Rhubarb and Garden Rhu- 

 barb (Rheum Officinale and Rheum 



Hybridum) (Illus.) 



Influence of Sunlight on Trees 

 Miscellaneous Notes... 



PAGE 



497 

 498 



499 



500 



5°3 



5°5 

 506 



507 

 508 

 509 



CONTENTS. 



PAGE 



Proboscis of the Elephant 509 



Poisons in the Workshop ... ... 510 



Reviews — 



Papers and Proceedings of the Royal 



Society of Tasmania, for 1887 ... 511 

 Primary Methods in Zoology Teach- 

 ing, for Teachers in Common 



Schools 511 



Star Atlas, containing Maps of all the 

 Stars from I to 65 Magnitude 

 between the North Pole and 34 

 South Declination, and of all 

 Nebulae and Star Clusters in the 

 same Region which are Visible in 

 Telescopes of Moderate Power ... 511 



Recognition of Human Blood 512 



Microscopic Manipulation ... ._ 512 



Action of Microbia on Colouring 



Matters 



Abstracts of Papers, Lectures, etc. — 



Society of Engineers 



Leeds Geological Association 



Australasian Association for the Ad- 

 vancement of Science 



London Mathematical Society 



Miscellaneous Societies 

 Foundation Stones of the Earth's Crust 

 Correspondence — 



The Martial Canals 



Recent Inventions 

 Sales and Exchanges ... 



Diary for Next Week 



Selected Books 



Meteorological Returns 



S«3 



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516 

 5.6 

 516 

 5i6 



51S 



5'9 



52,0 

 520 

 520 

 520 



SCIENTIFIC TABLE TALK. 



By W. Mattieu Williams, F.R.A.S., F.C.S. 



One of the common troubles to which laboratory workers, 

 and more especially laboratory martyrs {i.e., the hard- 

 worked, ill-paid, and unglorified assistants), are subjected 

 in the course of chemical work, is that of " bumping." 



Certain liquids must be boiled, continuously boiled, 

 in some cases to effect solution, in others for evaporation 

 sake. Docile solutions submit quietly and amiably to 

 such treatment; the bubbles of vapour are formed 

 immediately the boiling point is reached, they are small 

 and numerous, and detach themselves freely from the 

 heated sides of the containing vessel. But certain other 

 disagreeable liquids behave very differently. They rebel 

 against the discipline of boiling, sullenly persist in re- 

 maining calmly in the liquid form even when their tem- 

 perature is raised above their unquestionable boiling point, 

 clinging with stubborn tenacity to the smooth sides of 

 the heated vessel. Presently, however, their obstinate 

 resistance is overcome by the expansive energy of addi- 

 tional heat. 



The junior student who begins his work in qualitative 

 analysis by heating his solutions in test tubes, frequently 

 obtains a striking demonstration of the final result of 

 this contest. Finding that his solution does not boil in 

 accordance with his theoretical anticipations, he looks 

 down the tube to see what is the matter, when suddenly 

 a great bubble of vapour filling the lower part of the 

 tube is explosively formed, and more or less of the 

 liquid is projected to his face. As solutions of caustic 

 potash and soda, and of sulphuric acid (oil of vitriol), are 

 specially addicted to such proceeding, the demonstration 

 may be unpleasant to the operator, who speedily learns 

 to treat heated test tubes as old sportsmen treat gun 

 barrels ; he never presents their mouths towards himself 

 or his friends. 



In more advanced work, where beakers or flasks are 

 used, this sudden formation of the big vapour bubble and 



its collapse jerks the vessel on its stand with a violent 

 bump, from which the term " bumping" is derived. A 

 flask may thus be broken, and the work of a whole day, 

 or of several days, be thereby wrecked, or some drops of 

 solution may be ejected from an open-mouthed beaker or 

 evaporating dish, and thus a quantitative analysis be 

 altogether spoiled. The smoother and cleaner the con- 

 taining vessel the greater the liability— other conditions 

 equal — to this bumping, and in chemical analysis the 

 uttermost extreme of double-Dutch cleanliness must be 

 observed. 



If the vessel or liquid be decidedly dirty in the sense 

 of holding particles of foreign matter, bumping rarely 

 occurs, because the grasp of the liquid upon mere points 

 is very weak. This may be shown by boiling water or 

 any other liquid in a glass vessel which has one or more 

 projecting points of roughness on its surface. By watch- 

 ing them during the heating it will be seen that, just as 

 the liquid reaches its boiling point, streams of minute- 

 bubbles of vapour will pour from these points. The like 

 occurs when any other gas is disengaged from a liquid, 

 as, for example, the carbonic acid gas from champagne 

 or other sparkling liquid. Ordinary drinking glasses 

 commonly have such points on their surfaces, and from 

 these may be seen such issuing streams of gas bubbles 

 after the general effervescence has ceased. 



To prevent bumping, chemists have imitated this by 

 putting foreign solids into the liquid, solids that are in- 

 soluble and do not taint the liquid, such as pieces of 

 charcoal, platinum wire, etc. 



But there are some liquids that resist even these, or 

 in which their action is uncertain and variable. A 

 Russian chemist, W. Markownikoff, has lately struggled 

 with this practical problem, and finds that coating the 

 inside of the vessel with a thin deposit of silver is effec- 

 tive, but the silver film easily breaks off. His best results 

 were obtained by using very thin capillary glass tubes, 

 such as are easily obtained by heating an ordinary small 

 glass tube in a gas or spirit lamp flame, and drawing it 



