1867.] Physics. 553 



An apparatus for measuring the different degrees of trans- 

 parency of the air has been lately described by M. de la Kive, of 

 Geneva. According to M. de la Kive, the great transparency of the 

 air before rain is due to the presence in the air of a quantity of in- 

 visible vapour, which renders transparent the numerous germs 

 floating in the air, to whose presence light mists are attributed. 



Heat. — Gas has long been a common adjunct to English chemical 

 laboratories, and thanks to Mr. Griffin, the scientific man here is 

 provided with a multiplicity of gas furnaces, for obtaining all kinds 

 of results, from the slow evaporation of a pint of water to the fusion 

 of ten pounds of iron. In Paris, however, gas furnaces are only just 

 coming into vogue, and in their usual happy way our continental 

 confreres are rediscovering many forms of apparatus which are 

 well known here. At a recent meeting of the Academy, M. Debray 

 described two forms of apparatus for producing very elevated tempera- 

 tures by means of common gas mixed with air. The first was said to 

 be a form of M. Schlosing, modified by M. Wisnegg ; the second, that 

 of M. Perrot. If a certain number of Bunsen burners be united 

 together so as to form one single jet of flame, without, however, 

 complete incorporation, the heating power is most remarkable, pro- 

 vided a sufficiently energetic and swift draught is given to it. The 

 form of the furnace must also be varied, and the draught regulated 

 according to circumstances. With an apparatus burning 70 cubic 

 feet per horn, under a pressure of two or three inches of water, and 

 without any draught but that obtained by a sheet-iron pipe 6J feet 

 high, M. Debray was able, in fifteen minutes, to melt 148 lb. of 

 silver. It only takes half-an-hour at most, when the operation is at 

 full work, to melt and cast upwards of 2 lbs. of copper into a bar. 

 Lastly, M. Debray melted several specimens of grey and white iron. 

 A pound of a variety of cast-iron, which was considered very difficult 

 to melt, was run in thirty minutes; another piece, weighing Hlb., 

 was melted in an hour or so. During the operation, the crucible 

 can be examined in the interior by the aid of a mirror or a bucket 

 of water, which can receive the metal in case of accident. There 

 appear to be more points of novelty in this furnace than in most of 

 the French adaptations, but it is very similar to Gore's Gas Furnace 

 in its effects, and not unlike it in principle. 



The evaporation of large masses of liquids, simple as it may appear 

 on the small scale, is a formidable operation when many tons weight 

 of liquid have to be dealt with. M. E. Parion, at Wardrecques, St. 

 Omer, has invented a new process for the renewal of the surface of 

 the liquid exposed in the state of fine division in contact with the 

 air, or to the products of the combustion, according as the evapora- 

 tion should take place with or without the aid of artificial heat. 

 When the evaporation takes place by the aid of the temperature of 



2o2 



