24 The Progress of Physical Discovery. [JAN. 



Leslie, of Edinburgh, found means of augmenting the effect of the sup- 

 pression of air, by placing under the receiver of an air-pump substances 

 having a great avidity for moisture, which, possessing themselves of the 

 vapour as fast as it forms, multiply the production to any extent ; and 

 water is thus frozen in a very few minutes. Montgolfier, with the 

 improvements of MM. Clement and Desormes, contrived in this year a 

 method of drying the sugar of plants, and especially the juice of the 

 grape, by the air-pump. The utility of a process of preserving in a 

 small compass the alimentary substances of bodies, and the fermenting 

 matter that will yield wine and alcohol, is obvious, particularly for long 

 voyages and travels. The idea of heating by steam, first imagined by 

 Count Rumford in 1798, was this year applied to distillation with sin- 

 gular success, by a distiller named Adam, of Montpelier. He first con- 

 ceived the process of heating the wine put into distillation by the steam 

 of brandy which rises from the boiler, and of making this steam pass 

 through a series of vessels in which it deposits its aqueous parts, so that 

 the pure spirit of wine alone condenses itself in the last cooler. The 

 beneficial effects of chemical knowledge upon manufactures was never 

 more strikingly exemplified than by this method of distillation. Instead 

 of heating first to obtain brandy of 19 degrees, from which, by succes- 

 sive heatings, spirit was obtained of the required strength, the spirit is 

 by this made at once of any strength desired* Adam's still can be 

 heated eight times a day, while the old one could only be heated twice ; 

 it extracts a sixth part more spirit from the same quantity of wine, and 

 saves two- fifths of combustibles, and three-fourths of manual labour. 

 The results have already been highly beneficial to the wine districts of 

 France. Count Rumford, who has enriched physical science with so 

 many important discoveries in light and heat, this year turned his atten- 

 tion to the question which had divided the chemical world for more 

 than a century viz. Whether light is a substance which emanates from 

 luminous bodies, or a movement impressed by those bodies on a fluid 

 otherwise imperceptible and expanded throughout space ? Count Rum- 

 ford, after a variety of experiments with lamps and candles, found that 

 the heat disengaged in a given time was always in proportion to the 

 quantity of oil or wax burnt, whilst the quantity of light furnished in the 

 same time varied to an astonishing degree, and depended in particular 

 upon the greatness of the flame, which retards its cooling. Thus what- 

 ever can maintain the heat of the flame, contributes to augment its light ; 

 and Count Rumford, having constructed lamps, or flat matches placed 

 parallel to each other, which keep one another warm, made them pro- 

 duce a light equal to forty candles ; and he is of opinion that any degree 

 of intensity may thus be created. 



The theory of chemical affinity had until this year only been applied 

 to the reciprocal decomposition of soluble salts, and it remained to be 

 ascertained whether insoluble salts are not also capable of exchanging 

 their principles with certain soluble ones. A memoir was now presented 

 to the French Institute by M. Dulong, stating that he had arrived at the 

 result that all insoluble salts are decomposed by carbonates of potash and 

 soda, but that the mutual exchange of their principles can never, in any 

 case, take place completely ; and, on the other hand, that all soluble salts 

 whose acid forms an insoluble salt with the base of insoluble carbonates, 

 are decomposed by them, until the decomposition has reached a certain 

 limit which cannot be passed ; so that, in identical circumstances, com- 



