( 781 ) 



1 « — «„ 



transformation : for - hi. ^) was fcnmd a constant value wliicli 



t • ct^—a 



was the same in the ease of eillier isomer. 



This average value representing the sum of the velocity constants 

 of the two conlrary reactions is 0.0095 (the time expressed in hours 

 and using- ordinary logarithms) at 35° and a concentration of 27o zinc- 

 chloride. At 45° and 2"/„ ZnCI,, the average constant was 0.028. The 

 temperature coefficient of the transformation for every lO"" is, there- 

 fore, 3.01. Further detej'mijuitions were also made with l^/^ solutions 

 of zincchloride at 45° and the coustant was found to he 0.0135. 

 This seems therefore to be propoi-tionate to tiie concentration of 

 the catalyzer. 



5. Besides these two isomers, Tankkt (Bull. 1895, 13, 2t)l) ima- 

 gined to have found a third glucose-pentacetate. 



On treating glucose with acetic anhydride and a little yJiM'chloride 

 and recrystallising the product from alcohol, he ohtaijied from the 

 mother-liquor crystals with [«]^ ^ -[- 59° at 62'^. This sid)stance had 

 no sharply defined melting i)oint situated below the melting points 

 of the above isomers. As he could not etfect a further sepa- 

 ration of these crystals by recry stal lisat ion, he took it to be a third 

 modification with a melting point of about S(V, but still occluding 

 a small (piantity of the other two, Avhich it was difficult to get rid 

 off. It is however obvious that this so-called third moditication is 

 only a mixture of the other two. which is deposited from an alco- 

 holic solution saturated \vith both ('om[)oumls. The following facts 

 are in fa\our of this view. 



J'*^ If it were a third isomer, it might be got perfectly free from 

 the others by recry stallisation and present a delinite melting point. 



2"'*. If we make a mixture of the isomers melting at 134° and 

 112° so that [a]o = 60° the product will show the same melting- 

 traject as that of Tanket "'), namely 91—94°. 



3"'. A solution saturated with both isomers, and a saturated 

 solution of Tanret's product appear to contain the same amount of 

 pentacetate. 1 lla^'e used 50"/„ alcohol as solvent. On shaking at 25° 

 with an excess of the t\vo pure isomers a solution was obtained 

 containing 3.08 — 3.iO"/„ of pentacetate; Tanret's product similarly 

 treated gave a solution containing 3.13 — ^3.14*/,,. 



1) a' is the rotation in the condition of equilibiiuni, «„ the initial rotation, x 

 the same at a slated period. 



-) Mr. Tanret had the kindness to forward a specimen of liis preparation to 

 Prof. LoBRY DE Bruvn. With this sample the experiments have been made. 



