Page:Outlines of Physical Chemistry - 1899.djvu/190

 ��OUTLINES OF PHYSICAL CHEMISTRY

��These numbers were determined by Berthelot and Andri. They agree sufficiently well with those determined by Stohmann.

In the animal economy the combustion of albuminoids does not produce free nitrogen, but stops at the formation of more or less complex amido- compounds. In man 80 to 85 per cent, of the nitrogen is transformed into urea. If the nitrogen were wholly transformed to this, the heat of com- bustion of a quantity of the albuminoid substance contain- ing one gram of carbon would be reduced to 9 - 13 Cal.

Certain other elimination-forms of the nitrogen give rise to a still greater loss of heat, as the following table shows :

�� � � � �Organic Combustion oSltherabctuca

�Name

�Formula

�Total Oombna-

�nitrogen eliminated

� � � �moiecuLe

�from BerlMot mi petit or BerlMa

� � � �151-5 Cal.

�ani Ar-lri

�Urea.

�(

�_

�Uric acid

�c.

�3.

�461-4 „

�175-8 Cal

�Hipparic acid

�tit

� �1,0129 „

�982-8 „

�Glycocol

�c

� �234-9 „

�167-8 „

�Al&nine ,

�c;

�i

�3892 „

�327-5 „

�Lencin.

�c,

�855-9 „

�811-2 „

�TyroBin

�c,

�>.

�1,071-2 „

�942-6 „

��A general remark applicable to all these compounds (except urea and leucin) is that the observed heat of com- bustion is greater than the value calculated according to the hypothesis of Dulong (or of Welter). These scientists be- lieved that the heat of combustion of an organic body can be obtained by eliminating in the form of water as much hydrogen as possible, then adding together the heats of combustion of the residual hydrogen and of the carbon, both considered in the free state. According to this theory, the beat of combustion of a carbohydrate would be equal to that of the carbon contained in it (in reality, it is greater).

�� �