510 ILLUSTRATIVE EXPERIMENTS 



+ 0-002° in the cooling period a cooling curve may be constructed with the 

 temperatures from 0-9 to 2-9 as abscissae and cooling loss from — 0-002 to 

 + 0-002 as ordinates. The function is purely linear and extrapolation is 

 simple. 



Calculation of E.V. (a) Correction of Teniperature. From the cooling 

 curve it is easy to discover the loss of heat due to cooling in the ignition 

 period. This value should be placed in a third column for every temperature 

 recorded during the second and third periods. For any reading of the thermo- 

 meter, the total loss by radiation is obtained by summing up the losses in all 

 the preceding intervals after ignition, e.g. in the second period the losses were 

 -0-001, +0-001, 0-0015, 0-0016, 0-0018, 0-0018, 0-0019, 0-002, 0-002, 

 0-002, 0-002, 0-002. This gives a total loss of 0-0175 at the maximum tem- 

 perature observed. This value added to the observed temperature gives the 

 corrected temperature. The corrected temperature during the third period 

 varies so little that the arithmetic mean of the values is taken as the cor- 

 rected maximum temperature. In this case = 16-5325. 



(b) Calculation. 



Temperature before firing, 14-969. 



Temperature after firing (corr.), 16-5325. 



.". Rise in temperature, 1-5635. 



Water in calorimeter — 2,100 gram. 



Water equivalent of calorimeter = 767-5 gram. 



.•. Total water value = 2867-5 gram. 



Heat of combustion = 2867-5 X 1-5635 = 4484. 



Amount of N free food burned = 1-2 gram. 



.-. EV of food = 4484/1-2 gram. 



= 3737 cals. per gram. 

 = 3-73 Cals. per gram. 



As soon as possible after each estimation, the gases are let off and the bomb 

 opened. Wash out the bomb with dilute sodium hydrate to remove any 

 nitric acid formed, dry and replace the bottle containing soda lime. Close 

 the bomb. 



2. Gaseous Diffusion. 



Experiment on p. 38, Fig. 4. Try this first with coal-gas and then with 

 CO,,. Soak the porous pot in water and compare the rate of diffusion inwards 

 of carbon-dioxide with the outwards dift'usion of air. What part does 

 solubility play in dift'usion through a membrane 1 



3. Liquid Diffusion. 



Place a number of coloured solutions varying in nature and in concentra- 

 tion in test-tubes. Carefully fill the tubes with distilled water and note the 

 rate at which the colour diffuses upwards into the water (Fig. 5 (a), p. 39). 



(a) Nature. Use concentrated solutions of copper sulphate, potassium 

 bichromate, methylene blue, congo red, black Indian ink, etc. 



(b) Concentration. Take four test tubes and put 5 c.c. of distilled water 

 in each. To the first tube add 5 c.c. of cone. CUSO4 and mix thoroughly. 

 Remove 5 c.c. of this mixture and add it to tube 2. Mix and take 5 c.c. for 

 tube 3 and so on, rejecting 5 c.c. of the mixture in tube 5. This will give you 

 five samples of 5 c.c. each varying in concentration from tube 1, having 

 0-5 cone. ; tube 2 = 0-25, tube 3 = 0-125 and tube 4 = 0-0625. In tube 5 

 place 5 c.c. of the cone, solution. Now carefully fill the tubes with water so 

 as to form a clea r layer of water above the blue sulphate and measure the rate 



