CHAPTER V. 



EFFECT OF TEMPERATURE ON ABSORPTION SPECTRA. 



The purpose of the work on absorption spectra at high temperatures 

 was to obtain some knowledge of the chemical changes that take place at 

 these temperatures, by means of changes produced in the absorption spectra. 

 The cells used have, in the main, been the quartz cell and the two steel 

 cells described in a previous chapter. Some qualitative observations were 

 made with a hand spectroscope on solutions showing water and alcohol 

 bands. The work done with the quartz cell was mainly with acid solutions, 

 and this was done with a view to testing the stability of acid aggregates, as 

 will be explained a little later. Some work was carried out on the change 

 in the relative intensities of various solvate bands with change in temperature. 

 This will also be taken up in detail. 



The problem has been found to be a very difficult one, on account of 

 closing the cell tightly, and very largely because of the formation of precipi- 

 tates upon the windows of the cell. 



Some work has been done dealing with the effects of pressure and high 

 temperature upon solutions. W. N. Ipatieff 1 has shown that under a pressure 

 of about 125 atmospheres of hydrogen, anthracene and phenanthrene were 

 reduced, when heated in the presence of nickel oxide, to compounds such as 

 C 14 H 12 , C 14 H 14 , C 14 H 2(1 , etc. From this work and that of others it has been 

 shown that metals are precipitated from solutions of their salts by hydrogen 

 under pressure. There appears to be a critical temperature for the precip- 

 itation of each metal, silver and mercury being precipitated at ordinary 

 temperatures under a pressure of 200 atmospheres from a decinormal solution, 

 while copper and the more electro-positive metals could not be precipitated 

 even when the pressure exceeded 500 atmospheres. At 120 to 130, however, 

 branched crystals of copper were formed at 100 atmospheres; and at lower 

 temperatures cuprous oxide was formed. Cobalt was precipitated at 180 to 

 200, nickel at 200, lead and bismuth at 240 to 250, iron at 400 and 420 

 atmospheres. Ferric oxide was precipitated from an acetate solution at 350 

 and 230 atmospheres. 



Among some of the investigators who have studied the effect of pressure 

 and temperature on the conductivity of solutions are A. Bogojawlensky and 

 G. Tammann in 1898, and F. Korber 2 in 1909. In most cases the resistance 

 decreased as the pressure increased, but in many cases a minimum resistance 

 is reached, after which a further increase in pressure will cause an increase 

 in the resistance. This is true of solutions of potassium chloride at all tem- 

 peratures between and 100 C. At the minimum resistance is 0.872 of its 

 original value, and is reached at 3000 kg. per sq. cm.; at 100 C. the minimum 

 resistance ratio is 0.998 and this is reached at 900 kg. per sq. cm. Among 



1 Ber. d. chem. Ges., 41, 966 (190S); 42, 207S (1909). 

 Zeit. phys. Chem., 67, 212 (1909). 



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