( 268 ) 



substance, I)ut afler a few days exposure lo the air it again turns 

 faint 3'ellüw. 



An inn)rovenient was also desii-ahle iji the qnantitative detennina- 

 tion of benzidine. At first van Loon collected the j)recipitated benzi- 

 dine snlphate on a neighed filter, which was then dried at 100^ in 

 a steam oven and reweighed. Here Ave met with the unpleasant 

 fact that the filter often tnrned blackish probably owing to a decom- 

 position of the snlphate, which maj^ nnfavourabl}" affect the deter- 

 minations. The improved process now consisted in removing the 

 washed sulphate from the filter and boiling it with excess of standard 

 alkali. If now the excess of alkali is titrated at the boiling heat 

 with standard acid, the benzidine sulphate behaves like free sulphuric 

 acid when litmus is used as indicator. In this wny the determination 

 becomes more rapid and accurate. The usual correction for the 

 solubility of benzidine sulphate had, of course, to be made. 



The determinations made by Dr. van Loon of the ratio betweeji 



the quantities of benzidine and diphenjline formed during the 



transformation of hydrazobenzene by acids have demonstrated the 



influence of various circumstances on that relation and may be best 



represented in a tabular and graphical form. 



I. INFLUP]NCE OF THE CONCENTRATION OF THE ACID (HYDROCHLORIC ACID). 

 a) Solvent: Water. Temp. 18^—25°. 



^) Always percenls of weight arc meant. 



18* 



