Polytechnic Association. 769 



the simple experiment described in all text-books on natural philoso- 

 phy, in which water in a closed vessel, and near the boiling point, is 

 caused to enter into violent ebullition by the reduction of pressure 

 following the application of cold to the upper part of the vessel, 

 exhibits very plainly the probability of an action taking place such as 

 Colburn describes. 



The expulsion of the contents of a bottle of effervescent wine or 

 fermented liquor, which occurs frequently on drawing the cork, is 

 another illustration of such a phenomenon. There can hardly be a 

 doubt that cases do occur in which the same action greatly increases 

 the destructive effect of boiler explosions. 



In the case above considered, it seems probable that the effect of 

 the explosion was somewhat intensified by a generation of steam at 

 and near the exterior of the mass of water contained in the boiler, but 

 not by the expansion of steam formed near the center of the mass. 



Adjourned 



January 19, 1872. 



Professor S. D. Tillman in the chair ; Eobert Weir, Esq., Secretary. 

 Extract or Beef. 



Dr. P. H. Yan der Weyde exhibited a can of extract of beef from 

 Buenos Ayres, which he opened for examination. It is made upon 

 the same plan as Liebig's extract. The difference between the extract 

 of beef, diluted with hot water, and ordinary beef soup, is that the extract 

 of beef contains no gelatine. Gelatine is contained in bones, and affords 

 so little nourishment that it has been asserted that if the poor are fed 

 upon soup made largely from bones they will starve to death ; not that 

 the gelatine does any direct harm, but that it takes the place of nutri- 

 ment, while it is not nutriment. At Buenos Ayres meat is exceed- 

 ingly cheap. The finest cattle are killed simply for the skin and the 

 fat, the rest being thrown away. A company has been formed,, 

 which takes the beef and boils it down into beef tea, which is boiled 

 down until it is sufficiently thickened. It is derived from the muscle 

 of the animal, and contains no fat and no gelatine. The nutritive 

 power of the meat is considered to be concentrated into one-twentieth 

 its volume. It has been proved that in animals which have not yet 

 developed their teeth, the stomach is not capable of changing the 

 starch as it is required for digestion. Many children are starved to 

 death because they are fed with starch instead of beef tea or milk. 

 [Inst.] 49 



