554 Chronicles of Science. [Oct., 



the air alone, the liquids are divided into a small shower exposed to 

 the wind and sun. By maintaining them in this state we obtain in 

 a small space, and one easy to cover when necessary, the same 

 results as the concentrating basins and the graduating buildings 

 give at great cost and with a vast extent of land. In the case of 

 the employment of artificial heat, the waste heat from chimneys of 

 factories is utilized in preference, and in the absence of this any 

 source of heat is employed if the products obtained have a sufficient 

 value to pay the expenses. 



The artificial production of ice is a problem which has attracted 

 considerable attention of late years, and amongst the inventors of 

 practically useful pieces of apparatus, M. Carre is one of the most 

 successful. He has now described some new machinery for the pro- 

 duction of cold, based upon the rapid evaporation of water aided by 

 an air-pump and sulphuric acid. The apparatus would be difficult 

 to describe without the aid of diagrams, but we may state that his 

 air-pump is very cheap, and has worked without repair for eighteen 

 months ; the receivers for acid are formed of an alloy of lead and 

 antimony, which will resist for a number of years the attack of 

 sulphuric acid. The pump is made of copper, and the sides are 

 constantly coated with oil. The valves are moved mechanically. 

 The apparatus retains a vacuum for many months, and one kilo- 

 gramme of acid at 66° produces two or three kilogrammes of ice. 

 Freezing commences three or four minutes after exhausting. 



Electricity. — The theory of Grove's gas battery has occa- 

 sioned perhaps more discussion than that of any other instrument 

 of the electromotor class. When it was first described by the 

 learned inventor, M. Schonbein made certain objections to Mr. 

 Grove's explanation of its action; but these did not attract the 

 attentiou they deserved at the time. M. J. M. Gaugain has now 

 arrived at the same conclusion as Schonbein, using a different mode 

 of investigation. He only worked with one element at a time, and 

 instead of measuring the intensity of the current, he measured the 

 electro-motive force directly by the method of opposition. In this 

 manner the influence of the modifications which were successively 

 introduced into the arrangement of the couple could be numerically 

 estimated. The author explains how it is that Mr. Grove arrived 

 at a different result to his own. Mr. Grove considered it indispen- 

 sable that each of the platinum electrodes should be simultaneously 

 in contact with one of the gases and the liquid beneath. M. Gau- 

 gain finds, however, that when the platinum wires are immersed 

 completely in the liquid, and. therefore out of contact with the gas, 

 the electro-motive force is exactly the same as when arranged 

 according to Mr. Grove's principle. It follows therefore that the 

 action of the platinum only extends to the dissolved gas, and that 



