Clje $0}>ttlar Science jlttos 



AND 



BOSTON JOURNAL OF CHEMISTRY. 



Volume XXII. 



BOSTON, JULY, 1888. 



Number 7. 



COXTENTS. 



Familiar Science. — The Surface Tension of Liquids 97 



Optical Illusions 97 



Do Birds build bv Instinct, or Reason? 98 



The Golf. Ball's Flight 99 



American Indian Jugglery 99 



The Origin of Musk 100 



Scientific Brevities 100 



Practical Chemistry and the Arts. — Gas. Making.... 101 



Tile i'inhole Camera 101 



A Venetian Ship [tail way 102 



Ancient Materials for Paper-Making 102 



Detection of Cotton-Seed Oil in Ohve.Oll 102 



Industrial Memoranda 102 



Kaiiroad Xotes 102 



Home, Farm, and Garden. -Canned Goods 103 



Artificial Flavors 103 



Laund ry Suggestions 104 



Yankee versus European Cookery 104 



Gleanings 104 



Editorial. — Crysl alii zation 105 



Berlin Letter 106 



Astronomical Phenomena for July, 1888 107 



Meteorology for May, 1888, with that of the Spring 107 



'* How Birds Learn to Sing" 108 



Questions and Answers 108 



Literary Notes 108 



Medicine and Pharmacy. — Urea 109 



The Kind of Fruit Indigestible 109 



Some Fact* concerning Brigbt's Disease 109 



Monthly Summary of Medical Progress 110 



Care of the Ears Ill 



The Stimulus of a Change of Air ill 



A New Hypnotic 112 



Meclical iferaorandft 112 



Humors 112 



Publishers' Column 112 



familiar l)tttntr. 



THE SURFACE TENSIOK OF LIQUIDS. 



Ii' vvc place a piece of camphor upon a clean 

 surface of water, it will begin to move about 

 in various dir^tions, without any apparent 

 cause, and continue this motion for a long 

 while. By gently blowing upon it, the motion 

 may be increased ; and, singularly enough, the 

 camphor will move against the current of air, 

 being apparently atti'acted towards its source. 

 The same phenomenon may be observed when 

 the camphor is placed upon a clean surface of 

 pure mercury, previously slightly warmed. 



Fia. 1. 



The particles dart about in a most curious 

 manner, resembling the movements of little 

 tadpoles swimming in water (Fig. 1). If a 



drop of oil or any greasy substance is added 

 to the water in which the camphor is moving, 

 it immediatel}' stops. 



A curious toy depending upon this phenom- 

 enon may be made by bending a piece of tin 

 into the shape of a small boat, which may be 

 provided with a mast and flag (Fig. 2). A 

 piece of camphor is fastened to the stern, and 

 furnishes a motive-power which causes the 

 miniature ship to sail round in a most mysteri- 

 ous manner. The explanation of this phe- 

 nomenon is rather difficult, and, in fact, is 

 not perfectly understood by any one ; but it is 

 undoubtedly due to what is known as the sur- 

 face tension of liquids. 



We know that the surface of all liquids is in 

 a state of tension, like a piece of stretched in- 

 dia-rubber cloth. This surface tension of thin 



films is beautifully shown by a soap-bubble, 

 which, when blown, and allowed to remain on 

 the pipe, contracts upon itself, and gradually 

 grows smaller, like a toy balloon pierced with a 

 small hole. The current of air issuing from the 

 end of the pipe can be felt quite perceptibly, 

 and will affect a candle-flame very strongly. 



But this surface tension is not possessed by 

 a hollow sphere alone ; the surface of a solid 

 drop of water, or a mass of liquid of any 

 shape, exercises the same force, although it is 

 not evident, on account of the reaction of the 

 interior mass. 



This surface tension varies with dirt'erer 

 liquids, and is greatest in the case of water 

 If we spread a film of oil, alcohol, or eve 

 vapor of camphor, over the water, these films 

 displace the water-film, and reduce the surface 

 tension of the whole to that possessed by 

 themselves alone. 



The above considerations offer a very rea- 

 sonable explanation of the movements of cam- 

 phor upon water or mercury. Assuming the 

 surface of these liquids to be in a high state of 

 tension, the vapor of the camphor forms a film 

 of lower tension around it, as it rests upon the 

 water. If the tension was reduced regularly- 



in all directions, of course no effect would take 

 place ; but, as the vapor tends to spread more 

 or less irregularl}-, the tension will be greater 

 on one side, and thus cause a movement of 

 the piece of camphor. By blowing upon it, 

 the film of vapor is, of course, directed more 

 strongly in one direction, thus reducing the 

 tension of the water or mercury in the rear, 

 and allowing the water-surface in front to con- 

 tract more strongly, and pull the camphor 

 against the current of air. The effect can be 

 illustrated by placing a coin upon a sheet of 

 thin rubber stretched across a frame. While 

 the tension remains equal in all directions, 

 nothing takes place ; but if we cut through the 

 rubber directly behind the coin, the tension in 

 that direction is destroyed, and the contracting 

 rubber pulls the coin forward. 



It is only recently that this phenomenon of 

 surface tension has been fully recognized and 

 studied. It has an important bearing upon the 

 subject of molecular physics, and has a most 

 useful practical application in the use of oil as 

 a means of stilling the waves of a stormy sea, 

 which is undoubtedly caused by the difference 

 of surface tension between oil and water. The 

 subject is a most interesting one, and future 

 investigations upon it may greatly increase 

 our knowledge concerning the constitution of 

 matter in the liquid form. 



The accompanying illustrations are from an 

 article upon this same subject by M. Devaux 

 in La Nature. 



OPTICAL ILLUSIONS. 

 The stroboscopic circles (Fig. 1) were dis- 

 covered by Professor Thompson about ten 

 years ago. They are probably familiar to 



most of our readers ; but we may say, that, 

 when the drawing is held before the eyes, and 

 rotated with a sort of rinsiiig movement, the 



