104 PEOCEEDINGS OF THE AMERICAN ACADEMY. 



work again, we also obtained the trinitrophenylmalonic ester exclusively 

 in this form, and confirmed repeatedly the observations given above on 

 its crystalline form and melting point. Somewhat later we converted a 

 sample of the triuitrophenylmalonic ester into its very characteristic am- 

 monium salt, and upon acidifying this and recrystallizing the ester thus 

 set free we obtained instead of the rectangular plates four- (or six-) sided 

 plates in which two of the opposite angles were unlike, — one being 

 obtuse and the other acute, — so that the crystals were shaped somewhat 

 like a kite ; and not only did the form of these crystals differ in such a 

 marked way from the rectangular plates previously obtained, but they 

 also melted at G4° instead of at 58°. During this experiment a solution 

 of the ester from one of our preparations of it was evaporating spon- 

 taneously on the desk ; the next morning these kite-shaped crystals were 

 deposited from it, although it had previously yielded only the rectangular 

 plates melting at 58°, and since then we have obtained from all our 

 preparations only the form melting at 64°, whereas before exactly sim- 

 ilar pre[)arations had given us exclusively the form melting at 58°, as 

 Las been already stated. Varying the conditions of the preparations, 

 such as carrying them on in cooled or warmed solutions, or with longer 

 or shorter standing, did not modify the result, so that we have not suc- 

 ceeded in adding to the stock of the modification melting at 58°, which 

 we had on hand, when we encountered the other form. 



The following experiment seems to us to suggest a possible explanation 

 of these results : a solution of the form melting at 58° was evaporated 

 until it began to deposit the rectangular crystals, and then inoculated 

 with a speck of the form melting at 64°, when at once the kite-shaped 

 crystals of this form began to appear, and no more rectangular crystals 

 were produced. This experiment was tried several times early in our 

 work ; it could not be repeated later, as then recrystallization alone of 

 the form melting at 58° was enough to convert it partially or even com- 

 pletely into the form melting at 64°. As then a small amount of the 

 form melting at 64° is enough to convert a large quantity of the other 

 form into this, it seems probable that the small amount of the more 

 stable form floating in the air of the laboratory as dust was enough to 

 bring about this change, and to give us this more stable modification as 

 the sole product of our preparations, and even of recrystallizations of the 

 less stable form. The view that the inoculation of the solutions pro- 

 ceeded from the dust in the air is supported by the following observa- 

 tions. A preparation made with new apparatus and fresh material, 

 but in the laboratory where these experiments had been tried, yielded 



