Lavoisier, about 1777, advancing from the quantitative study of one chemical change to another was able to describe many processes, and to distinguish between an element and a compound. He cast aside all the alchemical formulæ and expressed the results of his experiments in fractions and proportions. J. B. Richter between 1791 and 1802 made a series of experiments by which he secured the weights of various bases neutralized by constant weights of several acids, and the weights of several acids neutralized by constant weights of several bases. He found that the composition of chemical compounds is constant, as had been assumed by Lavoisier and Boyle. Dalton described the atomic constitution of gases in 1808, and sketched the law of multiple proportions in chemical combinations and described binary, ternary and quaternary combinations. Prussic acid was investigated by Gay-Lussac in 1815, when he isolated cyanogen and found that although it is a compound it plays the part of an element with hydrogen and the metals. Berzelius also found that ammonium possessed all the properties of an alkali metal. Ten years after the above discoveries were made, Faraday prepared a compound of carbon and hydrogen from liquefied coal gas which led to the general study of isomerism and the great discoveries of the organic radicals with their important combinations. When isomeric combinations were studied by Jacob Berzelius (1779-1848), he was led to devise a means of expressing organic reactions. He wrote to Wöhler and Liebig a letter outlining his new method in which he said: "From the moment when one has learned to recognize with certainty the existence of ternary atoms of the first order which enter compounds after the manner of simple substances, it will be a great relief in the expression of the language of formulæ to denote each radical by its own symbol, whereby the idea of composition it is desired to express will be placed clearly before the eye of the reader." [Illustration: Photo, Fifth Avenue Hospital ROOM IN WHICH INFECTED ARTICLES ARE STERILIZED] [Illustration: MODERN OPERATING ROOM IN A PARIS HOSPITAL. IT IS FITTED WITH A GLASS DOME AND RADIO MICROPHONES FOR THE USE OF STUDENTS AND DOCTORS WHO WISH TO WATCH THE OPERATIONS AND HEAR DISTINCTLY THE COMMENTS OF THE SURGEONS] An example of this method of expressing reactions was given in the case of the action of chlorine on benzoic acid. He wrote B₂O for benzoic acid, B₂CL₂ for chlorbenzol and B₂ + NH₂ for benzamide. With certain simple improvements made subsequently by Gmelin, the method devised by Berzelius was generally adopted and is in use to-day.