218 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



were formic, acetic, and butyric. The author shows that if 

 the measured surface tensions of these liquids be taken as 

 ordinates, and the percentages by volume of the liquid as ab- 

 scissas, the resulting curve resembles an elongated parabola, 

 or, more exactly, an exponential curve, the equation of which 

 he gives. Methyl and ethyl alcohols have a point of inflec- 

 tion in their curves. From his results he formulates the fol- 

 lowing important law : If with the different alcohols or the 

 different fatty acids mixtures be made in various propor- 

 tions, and if those mixtures are compared together which 

 have the same surface tension, the percentage ratios of alco- 

 hol or of acid which they contain are constant, and inde- 

 pendent of the actual value of this tension. 



3. Of Gases. 



Stearn & Swan have improved the Sprengel air-pump by 

 closing the reservoirs at top and bottom, so that no pressure 

 is exerted on the surface of the mercury by the external at- 

 mosphere. In consequence, the fall tube may be very much 

 shortened without impairing the efficiency of the instru- 

 ment. On beginning exhaustion, the mercury reservoir at 

 top is filled, and closed by a stopper, and, by means of a small 

 exhausting syringe attached to the lower reservoir, a con- 

 siderable portion of the air is removed from the receiver to 

 be exhausted, and the pressure on the mercury in the lower 

 reservoir is materially reduced. The flow of the mercury in 

 the pump completes the exhaustion rapidly. With a fall 

 tube only nine or ten inches long, a small vacuum tube fur- 

 nished with aluminum wires separated by a quarter inch was 

 exhausted in twelve minutes so perfectly that an induction 

 coil giving half- inch sparks in air failed to produce the 

 slightest luminosity. The new form of pump is for sale by 

 Mawson & Swan, of Newcastle-upon-Tyne, at the price of 

 7 105. sterling. This firm also make a compound pump of 

 this sort having three fill tubes, by which the exhaustion is 

 very much accelerated, at the price of 9. The small vacu- 

 um tube, which was exhausted with the former instrument 

 in twelve minutes so perfectly that an electric spark of half 

 an inch in air would not pass through it, was exhausted with 

 the compound pump in three minutes. 



Puluj, of the University of Vienna, has published the sec- 



