STAINING, PRACTICAL AND THEORETICAL 



Some observations 



on 



THE EFFECTS OF HEAT ON THE pH OF AQUEOUS DYE 



SOLUTIONS 



Following the syntheses of the Falgic acids in vitro (Gurr and 

 MacConaill, 1959, i960; MacConaill and Gurr, i96o«), the present 

 author decided to make further investigations into the mechanism 

 of the chemical reactions involved. In this later work it became 

 necessary to make accurate pH measurements, over a wide range 

 of temperatures, of aqueous solutions of certain acid dyes. Basic 

 dyes were not investigated at the time, but work on these is being 

 carried out in the author's laboratories at the present time and 

 the results will be published elsewhere when the investigations 

 have been completed. 



The acid dyes investigated registered pH values over a range of 

 approximately 2-5-4'0 for 1% aqueous solutions in distilled water 

 at 20° C. In these experiments it was observed that as the tem- 

 perature of the dye solution was gradually increased up to about 

 60° C so the pH shifted over to the more acid side As the tem- 

 perature was gradually increased still further, the pH became less 

 acid, until at 100° C the dye solutions registered the same pH 

 values as those observed at 20° C. The solutions were then 

 allowed to cool gradually to room temperature (20° C), and it was 

 noted that during the cooling process the same pH changes took 

 place but in reverse, so that at 20° C the pH readings were identical 

 with those originally observed before the solutions had been 

 heated . 



It should be mentioned here that the necessary adjustments 

 were made to the pH-meter to allow for readings over a tempera- 

 ture range of o°-ioo° C. 



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