314 Domestic Science 



change of colour may be seen with greater ease if 

 a small white tile be placed under the beaker during 

 the operation. Throw away the contents of the beaker, 

 rinse it out two or three times, and then pipette into 

 it a further 20 c.c. of the alkali. Colour this with 

 litmus solution. Run in 1 c.c. less than the total 

 quantity used in the previous operation, and then 

 let the acid drop in, one drop at a time, stirring after 

 each drop. As soon as the colour change occurs, 

 stop the addition of acid, and read from the burette 

 the exact volume used. This is the volume required 

 to " neutralise " 20 c.c. of the potassium hydroxide 

 solution, and the operation is termed " neutralisation ". 

 If a third determination be made as directed in the 

 second case, the reading obtained should agree very 

 closely within 0-05 c.c. with that noted in the second 

 operation. 



Pipette 20 c.c. of the alkali into a beaker, and add 

 from the burette the amount of acid which has been 

 found to neutralise it. Evaporate this solution and 

 crystals of potassium sulphate will be obtained. 



EXPERIMENT 145. Put 20 c.c. of the potassium 

 hydroxide used in the previous ex- 

 periment into a beaker. Add twice 

 the volume required for neutralisation 

 of the same acid as used before. 

 Again evaporate and crystallise out. 

 If crystals of sufficient size be ob- 

 tained, compare the shape of those 

 formed in Experiment 144 with that -pig. 102. 



of those now obtained. They will 

 be found to bear little resemblance to one another. 

 The usual shapes of each kind of crystal are illustrated 

 in Fig. 102. We have thus prepared two substances of 



