286 Conductivity of Aqueous Solutions. Part IX. 



diketotetrahydrothiazole was the most suitable acid. This acid has also 

 been called dioxythiazole and mustard-oil acetic acid, and has, according to 



CO CH 2 _ 

 the investigation of Hantzsch * the structure! I S. The base 



NH CO- 

 has at 25 an ionization-constant of 18.1 X 10~ G and the acid one of 

 0.181 X 10~ G , and their salt a hydrolysis of about 4 per cent, as the meas- 

 urements presented below show. This base is more easily obtained pure 

 than any other base of similar strength ; and the acid can be readily pre- 

 pared in quantity from thiourea and chloracetic acid. It is, however, so 

 weak, that its salt is about ten times as much hydrolyzed as ammonium 

 acetate (which is 0.4 per cent hydrolyzed at 25) ; and yet it is strong 

 enough to have a conductance which can be fairly accurately determined, 

 though it lies near the limit in this respect. 



In detail, therefore, this investigation has consisted in the preparation 

 and purification of the diketotetrahydrothiazole and the determination of 

 its ionization by conductivity measurements at 0, 18, and 25 at various 

 concentrations, in corresponding measurements with ammonium hydrox- 

 ide, and in measurements at these three temperatures of the conduct- 

 ance of the salt at 0.02 and 0.05 normal both in water alone and in the 

 presence of about the equivalent amount and half the equivalent amount 

 of the free acid and of the free base in separate experiments. In order 

 to determine the conductance of the completely ionized acid and salt, 

 measurements were also made with the latter at a concentration of 0.002 

 normal. 



100. PREPARATION OF THE SUBSTANCES AND SOLUTIONS. 



The diketotetrahydrothiazole was prepared as described by Volhard$ 

 by heating together thiourea and chloracetic acid in aqueous solution. 

 The product was purified by a large number of crystallizations from 

 methyl alcohol and from water. No boneblack was used. The crystalli- 

 zation from water was continued until the sample was perfectly white 

 and no further change in conductance was produced, as will be shown 

 in section 102. The last crystallizations were made from conductivity water 

 in platinum vessels, and the crystals were filtered out and dried at 100 

 in a platinum Gooch crucible in purified air. A portion of the product 

 so dried was finely powdered and kept in a desiccator over sulphuric acid 

 for several weeks ; it lost only a few hundredths of 1 per cent in weight, 

 showing that it was dry. The melting-point of the purified sample was 

 found to be 123.4. 



*Ber. d. chem. Ges., 20, 3129 (1887). 



fEven assuming that this substance exists in part in the desmotropic "enol" form, 

 this would make no difference in the values of the ionization of water derived from 

 the study of its equilibria ; for the concentrations of the two forms must be under 

 all circumstances proportional to each other. 



$J. prakt. Chem. (2) 9, 6 (1874), 



