Aug. 31, 1888.] 



SCIENTIFIC NEWS. 



201 



EXPERIMENTAL PHYSICS. 



Tl ERE is a carafe with a wide neck, which we hold 

 J- -L horizontally, having placed a cork loosely inside 

 its neck. " Will you," we said to a young student of 

 physics, " attempt to blow upon the cork ? We defy you 

 to drive it into the carafe." Our friend took the carafe in 

 one hand, as shown in the figure ('from La Nature), and 

 with the calmness of a man sure of success, puffed 

 out his cheeks, filled his mouth with air, and blew strongly 

 upon the cork, believing that he could drive it to the 

 bottom of the bottle. The instant he blew, the cork, 

 as if projected by a spring inside, issued violently from 

 the mouth of the bottle and struck the experimentalist on 

 the lips. 



The explanation of the phenomenon is easy : on blow- 

 ing into the confined space within the -bottle, the internal 

 air is compressed, and then, expanding again, throws out 







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Bottle Experiment. 



the cork, the projection of which will be more energetic 

 the more strongly the experimentalist has blown. 



Some precautions are necessary for success : the 

 carafe must be perfectly dry, especially in the neck, as 

 moisture might cause the cork to adhere, and it must also 

 be very smooth. 



AUTOMATIC CONSTANT-LEVEL 

 BALANCE. 



THE analysis of potable or of mineral waters generally 

 requires the evaporation of 2, 5, 10, or perhaps even 

 20 litres of water, and when it is required to ascertain 

 the residue per litre, or to determine the silica, we must 

 operate in a platinum dish, the use of porcelain or glass 

 not being possible. This operation must also be con- 

 ducted with care, because brisk ebullition might occasion 

 a slight loss, especially in case of a magnesian water. All 

 spirting must also be avoided. The appliances devised 

 for this purpose not working satisfactorily, M. Charles 

 Truchot proposes, in La Nature, the apparatus of which 

 we copy the figure and description. It consists 

 essentially of an ordinary balance supported on a pillar 

 and corresponding in size with the capsule to be used. 



One of the pans is substituted by a piece of wire gauze 

 upon which is set the capsule. In the other pan are put 

 weights so as exactly to counterpoise the capsule. By 

 means of a slight modification in the fork, which checks 

 the oscillations of the beam, a narrow caoutchouc tube 

 may be compressed between the beam and this fork. 



The tube communicates, on one hand, with a Mariotte's 

 bottle containing the water to be evaporated and the 

 bent end of which ends above the capsule. Things 

 being thus arranged the water will flow into the capsule 

 as soon as its weight is insufficient to overbalance the 

 counterpoise. This counterpoise is so arranged that 

 when the capsule is three-fourths full it slightly pre- 

 ponderates. The beam then lowers, pinches the 

 caoutchouc tube, and the flow of water stops. If there 

 is a gas burner placed below the capsule, as in the figure, 

 the evaporation soon begins, the capsule becomes lighter, 



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Automatic Balance. 



the beam rises, ceasing to press upon the flexible tube, 

 and the water flows again. 



Experience shows that the apparatus is self-acting, so 

 that the water falls- drop by drop at the rate of 30 — 60 

 drops per minute according to the rapidity of the 

 evaporation, so that the level is kept constant. The 

 level depends simply on the tare and the number of 

 drops must depend on the intensity of the evaporation, 

 consequently on the temperature applied. 



If it be feared that the supply may cease when the 

 bottle is empty and the deposit may be calcined the other 

 end of the fork may be made to pinch the tube which 

 supplies gas to the burner. If the capsule is not supplied 

 the gas flame lowers and is extinguished before the 

 deposit becomes dry. 



ODOURS, AND THEIR FUNCTIONS. 



THAT almost all plants and animals throw off 

 volatile matters which affect our sense of smell is 

 a fact perfectly admitted. That the more susceptible 

 olfactory organs of certain lower forms of life will be 

 more vividly impressed than our own will also not be 

 disputed. But when we come to ask why this or that 



