506 ILLUSTRATIVE EXPERIMENTS 



81. Iron. 



82. Sulphur. 



83. Purple of ( 'assius. 



84. Gelatin, 1 per cent. 



85. Starch, 1 per cent. 



86. Gum mastic. 



87. Silicic acid. 



• 88. Coarse suspensions. 



89. (i.) Egg albumin from eggs. 



(ii.) Egg albumin from commercial egg albumin. 



90. Finely divided suspensions of protein for use in experi- 

 ments on proteases. 



(6) Gels. 



91. Egg albumin. 



92. Gelatin. 



93. Preparation of non-polarisable electrodes. 



94. Graphic conversion of Sorensen's pH into concentra- 



tions of H ions. 



95. Estimation of the surface area of the body. 



VARIOUS CONVERSION FACTORS 



Graphic conversion of S0rensen's pH into concentrations of hydrogen ions, 



and the reverse (Eoaf). 

 Estimation of the surface area of the body. 

 Conversion factors. 

 A list of some practical handbooks. 



I. Bomb Calorimeter. 



Measurement of E.V. of Foods by Calorimetric Combustion. — The prin- 

 ciple underlying this method is the combustion of a known amount of 

 the material in an apparatus so devised that practically all the heat evolved 

 is absorbed by a known amount of water and by the apparatus itself (which 

 is of known heat capacity). Some form of bomb calorimeter is now univer- 

 sally employed for this purpose. The instrument (Fig. 3, p. 24) consists of 

 three main parts. 



1. The bomb itself (Fig. 102) is constructed of steel, nickel-plated, with a 

 cover to be screwed on firmly against a lead washer. It is lined with a special 

 enamel to resist corrosion. Its capacity is about 400 c.c. Through the cover 

 the entrance and exit gas channels pass ; K2 with its continuation platinum 

 tube, R, is for the introduction of oxygen, and /il for the withdrawal of the 

 gaseous products of combustion. Both channels are closed by means of the 

 screw spindles VI and V2, running in stuffing boxes. >S1 and 82 are screws 

 to stop the lateral communication with /il and K2. Throush the centre of 

 the cover passes a strong platinum wire, D, and this, as well as R, is fitted 

 with short pegs, a}, a^, on which hangs the crucible T. A short collar, just 

 above these pegs, is for the attachment of the ignition wire. PI and P2 are 

 two small screw-clamps for attaching to the electric wires for ignition. 



2. The insulating chamber is a double- walled copper vessel of about 

 11 litres capacity, and the space between the walls is to be filled with water 

 at room temperature. It is lined with white enamel, and contains within it, 

 but insulated from it by a thin ebonite stand, 3, the water holder or calori- 

 meter vessel. 



