ADVERTISEMENT

Chemical Progress

The work of Berthelot, Mendelliff and moisan

WITHIN the past twelve months three great chemists—Berthelot, Mendeleeff and Moissan—have died. In a series of leetur.es before the Royal Institution in London Sir James Dewar has referred to the work of these men; we abstract portions of his lectures from the columns of our London contemporary, Engineering. These three men were giants who represented three different types of mind—Berthelot was a colossus, to be compared to Liebig, without any modern parallel; Mendeleeff, the suggestive idealist; Moissan, the pure experimentalist. Marcellin Berthelot was born in 1827. When engaged in his first research, the study of the constitution of the fats—which are salts or esters of the fatty acids (stearic, palmistic, oleic acids, etc.) and of a trivalent alcohol, glycerin—he did not content himself with decomposing (saponifying) the fats by means of caustic alkali (steam or acids are technically used now to effect the same saponification). This decomposition yielded the alkali salt of the organic acid (a soap) and free glycerin. Berthelot also recombined fats from their constituents, prepared new fats, and further investigated the equilibrium of the reaction. He recognized that the reaction would proceed for a certain time in the desired direction, as decomposition, e. g , but the decomposition would not be complete. When certain proportions—depending upon the presence of water and other substances and on various conditions—had been reached, the action might reverse. Building up a body from its constituents was known as a synthetical process, and these researches led Berthelot to perfect syntheses; that is, the preparation of organic substances from elementary substances— charcoal, air, and hydrogen. Passing alcohol through red-hot tubes, he obtained complex substances; but the alcohol had itself first to be synthetized. The simplest organic acid—formic acid, or, rather, its alkali salt—he obtained from carbon monoxide (CO) and caustic potash; the acid itself should result from the combination of CO and water (H,O), but these two would not combine. The formic acid was a starting point. By heating barium formate, he generated marsh gas (CH,), which further heating, or electric sparking, converted into C,HL,, C,H., , C,H, and higher hydrocarbons, finally. naphthalene (C",H, 1. The direct combination of carbon and hydrogen gave another starting-point. As these elements would only combine at high temperatures which destroyed the resulting product—acetylene—he passed hydrogen through a bulb in which an electric arc was maintained between carbon electrodes, and withdrew the acetylene at once from the bulb. The demonstration of this very slow reaction was accomplished by cooling and condensing the little acetylene obtained in a U-tube; on warming this tube afterward by the heat of the hand, the colorless hydrogen flame changed into the bright acetylene flame. As acetylene readily polymerized (its molecules unite to form higher compounds), and as it was also easily oxidized, further syntheses opened up. But Berthelot failed, even in his renewed attempts, in the last weeks of his life, to effect a direct combination between carbon and nitrogen in the absence of other elements. He did obtain prussic acid, however, from carbon, nitrogen, and hydrogen. This demonstration was accomplished with the aid of an electric arc in another bull:,; and as this acid yielded with water ammonium formate, ammonia could also be introduced into the other synthetically prepared bodies. While engaged in these remarkable researches Berthelot also placed thermochemistry on a sure basis, working, at first, unaware of the simultaneous investigations of .Julius Thomsen (of Copenhagen), and from thousands of observations of the heats of combination of all kinds of bodies, arrived at the conclusion that when two or more bodies react, those bodies will result which, by their formation, produce the maximum amount of energy. The lecturer showed how the Berthelot calorimetric bomb is used. The bomb is a two-part vessel of steel, screwed up. in which substances or mixtures are burned or exploded by chemical or electrical means, after immersing the bomb in a calorimeter. In the demonstration of the complete combustion of an organic substance with oxygen mder a pressure of 25 atmospheres, the temperature of the water rose slowly at first, rapidly afterward. 'Sir .James also demonstrated how the velocity of an explosive wave was measured hy Berthelot. The two ends of a coiled pipe were bent upward; the gas mix- lure was fired at one end by an electric spark. and immediately afterward the fiery wave appeared at the other end; the time interval could be measured by a chronograph. The coil used was immersed in liquid air to retard the reaction. In his eightieth, and last ye4r, Berthelot was engaged in studying the heat of hremoglobin (the chief constituent of the red blood corpuscles), the absorption of carbon dioxide by plants, the heat evolution of radium, and the reactions produced by the silent electric discharge in his (Berthelot) tubes. Berthelot, it will be remembered, was French Secretary of Foreign Affairs for some time. Dmitri Ivanovitch Mendeleeff was a man who had conducted many series of painstaking studies, but he was essentially a seer, essentially proud, and proud of his having been a seventeenth child; a man of refinement, an idealist, but very careful to verify his speculations by experiments. Mendeleeff first studied crystallography and isomorphism, and then the relations l}etween the pressure p and the volume v of liquids. He recognized that every liquid has an absolute boiling point (the critical temperature of Andrews), above which no liquid can exist as such, and he gave the formula V; =1/(1 — kt). This formula was less perfect, than the one proposed by an Edinburgh bookseller, Waterston, at the same time; Vi = a — b log (T — t), where T is the critical temperature; but the papers which Waterston sent to the Royal Society were not heeded until Lord Rayleigh had- them published later. Mendeleeff then turned to gases. That the p v could not be constant was clear, since that meant that finally the gas could not occupy any volume at all. Hence Mendeleeff argued, there must be a minimum volume for a gas, and similarly a maximum volume; that is to say, a gas will not at any reduced pressure expand to an unlimited amount. That the first part of the argument was correct is proved by the work of Reg- nault, Amagat, and Andrews on the p v curves, which, as Mendeleeff foreshadowed, all became finally straight parallel lines, while at first there was a decrease in the p v for all bodies (with the exception of hydrogen, whose p v was a straight line from the beginning). But the latter argument, the upper limit of expansion which Mendeleeff attempted to demonstrate by experiments on a big scale, we do not now believe to be correct. These researches brought Mendeleeff to a study of the atmospheric circulation. Having visited the petroleum wells both at Baku on the Caspian, and in the United States, he recognized the broad difference in the composition of the two natural oils, and expressed the opinion that while the American oil, which seemed to be confined in relatively small natural reservoirs that were soon exhausted, might be of animal origin, the Balm petroleum was probably the product of the decomposition of metallic carbides, of which we knew very little in those days. Passing to the periodic law, with which Mendeleeff's name will remain pre-eminently coupled, classifications of the elements had been based by Dumas and others on the striking analogies presented by oxygen, sulphur, selenium, and tellurium, and their compounds, and by other families of elements. Following unknowingly in the wake of Newlands, Mendeleeff—and Lothar Meyer similarly at the same time—arranged the elements in twelve series of groups of seven or more elements, according to increasing atomic weights. The task was far bolder, Sir .James said, than it appeared to-day; for the constants of the elements, which he regarded as periodic functions of the atomic weights, were less perfectly known then. Yet three lacunre in the table were soon filled up, as predicted by Mendeleeff. by the discovery of three new elements (scandium, gallium. and germanium ). and his corrections of several atomic weights which did not fit his table were proved to be justified. Mendeleeff, Sir .James stated, was not easily disturbed in set views. The rare earths were accommodated in his table, and room was found for the new gases as well by placing helium. atomic weight 4; neon, 20; argon, 40; krypton, 82; and xenon, atomic weight 128, at the heads of the old groups. In one of his latest speculations Mendeleeff suggested a chemical conception of the ether as a legitimate extension of his periodic law. Two more elements remained to be discovered, one of atomic weight 0.4 (hydrogen = 1), the other lighter even ' than the corpuscles or electrons, a kind of neutral substance that would not be attracted by the sun. Henri Moissan was born in 1852, at Paris. To Moissan belongs the credit of having rejuvenated inorganic and mineral chemistry in our age of organic chemistry. A pupil of Fremy and Deville—both famous inorganic chemists by the way—Moissan first studied the evolution of oxygen and of carbon dioxide by plants in the dark, investigated the oxides of the iron metals, and then took up the isolation of fluorine, which so many distinguished experimenters had tried before him. The alchemists knew that sulphuric acid attacked fluorspar, and generated from it a gas which corroded glass; the electrician Ampere first pointed out the analogy between hydrochloric and hydrofluoric acids. Kemp made vessels of fluorspar for the acid, which is now kept in paraffined bottles. Moissan elec- trolyzed perfectly dry hydrofluoric acid in a U-tube of copper (originally platinum was thought indispensable), with plugs of fluorspar for the platinum electrodes, and two outlets, the one for the hydrogen, the other for the fluorine. The fluorine gas passed through a coil which, like the U-tube, was immersed in solid carbon dioxide to condense the fluorine, and through two tubes filled with sodium fluoride to absorb traces of the gas. The gas had a faint greenish-yellow color, and attacked almost everything; finely-divided carbon burned in the gas, forming a compound analogous to carbon tetrachloride (C C1], colorless liquid, which we could not prepare synthetically out of C and Cl, however. That fluorine formed a similar volatile compound with silicon was shown with the aid of some fluorine gas inclosed in glass pipettes, sent by Prof. Lebeau—Moissan's former assistant in these and other researches. The perfectly dry gas did not attack glass. Dwelling on the analogies between fluorine, chlorine, bromine, and iodine, which form the so-well-characterized group of the halogens, Sir James showed that chlorine gas could easily be condensed to a yellow solid, and bromine to a red solid. The melting points of the four elements were in deg. Cent.: F —215, Cl — 102, Br — 7, I + 114; the boiling points in the same order, — 187, — 33.6, + 58, + 184 deg. C.; the specific gravities, 1.14, 1.56, 2.95, 3.38; and analogous gradations were found to hold for the atomic weights, 18.91, 35.74, 79.84, 125.89; the atomic volumes, the atomic refractions, etc. Again, a similar gradation was observed in the properties of the compounds, except that the boiling point of hydrofluoric acid ( + 19.4 deg. C.) was too high, probably because this acid polymerized. A study of the physical and chemical constants of certain organic (benzene) compounds of fluorine had, however, misled chemists in ascribing to fluorine a higher volatility than to hydrogen; fluorine could be condensed at about —215 deg. C., as mentioned already. The enormous activity of fluorine was marked hy the number of heat units liberated—according to Ber- thelot—when fluorine and hydrogen combined to hydrofluoric acid (HF)—viz., 38,600—while the formation of H Cl only liberated 22,000 heat units. Now solids hardly reacted on one another under ordinary circumstances, and we had every reason to believe that at absolute zero temperature all reaction must cease. As, however, fluorine still attacked the hydrogen of organic compounds when they were kept in liquid air, Moissan had doubted that fluorine would really become inactive at the lowest procurable temperatures. In 1897, therefore, Sir James Dewar and Mr. Lennox tried whether fluorine could be solidified, and how it would behave then. The fluorine did freeze at 20 deg. or 30 deg. absolute; but when liquid hydrogen was dropped on the solid. the whole apparatus was shattered to fragments. We thus had a proof, at any rate, that fluorine was the most active body. With graphite, however, fluorine only combined when the graphite was red-hot, with diamonds not at all. But graphite, and not diamond, was the most stable modification of carbon at high temperatures; and as minute diamonds had been found associated with other carbon, in meteorites, Moissan started on his preparation of artificial diamonds by melting iron and carbon (carbonized sugar) in a crucible, and dropping the fused mass into water. The iron would expand on solidification, and the chilled outer crust would subject the still liquid solution of carbon in iron inside to an enormous pressure. Sir .Tames mentioned' Moissan's preparation of the hydrides of potassium (KH), cresium, and rubidium—snowy crystals, representing alloys of the metal and hydrogen, which did not conduct the electric current any more than hydrogen did—and to the many products which Moissan prepared in the electric furnace. Of the carbides, those of lithium, calcium, strontium, and barium yielded on decomposition with water, acetylene C,H,; aluminium carbide gave marsh gas (CH,); manganese carbide yielded C H, and hydrogen; the carbides of the rare earths cerium, yttrium, thorium yielded C, H", CH” ethylene C, H.,, and some liquid paraffins; while the carbides of chromium, molybdenum, titanium, and zirconium were not decomposed by water, so far as it had yet been discovered. It is reported that in 1908 Canada will make her own coinage, amounting to sixteen or twenty million pieces annually. The Royal Mint in London now coins sixteen million pieces for Canada per annum. When the new Canadian Mint opens, probably in December next, one or more new coins will be issued. A new two-cent piece will be coined in nickel. This will be the first time that nickel has been used in Canadian coinage, although it Is one of Canada's mostly largely produced minerals.

Scientific American Back To School

Back to School Sale!

12 Digital Issues + 4 Years of Archive Access just $19.99

Order Now >

X

Email this Article



This function is currently unavailable

X