GELATIN AND POTATO MEDIA. 



155 



For practical purposes it is sufficient to dissolve 40 g. of 

 sodium hydrate in distilled water, and to dilute this solution 

 to one liter. This will give an approximately normal solu- 

 tion. 



2. One that will contain 

 4 g. of this base in one liter 

 of water. This is known as a 

 deci-normal (ft) sodium hydrate 

 solution. It is prepared by 

 taking 100 c.c. of the normal 

 solution, and diluting- this 

 with distilled water to one 

 liter. It is evident that this 

 solution has one-tenth the 

 strength of the former. These 

 two solutions are placed in 

 the apparatus shown in Fig. 

 24. This consists of two 

 burettes, each of 50 c.c. capa- 

 city, graduated in T<T c.c., and 

 connected with bottles or 

 flasks which contain the nor- 

 mal and decinormal solutions, 



reSDCCtivelv FIG. 24. Burettes for titrating nutrient 



media, a Connected with stock of ft NaOH 



Titration Of the Gtelatin. Bv solution. Connected with stock of 



J N NaOH solution (F.G.N.). 



means of a pipette measure 



out 10 c.c. of the gelatin solution into each of four test- 

 tubes, and label these 1, 2, 3, and 4. 



To tube 1 add 2.5 c.c. of the ft NaOH solution. 

 To tube 2 add 2.8 c.c. of the ft NaOH solution. 

 To tube 3 add 3.2 c.c. of the & NaOH solution. 

 To tube 4 add 3.5 c.c. of the ft NaOH solution. 



Heat each tube in the flame till the liquid boils, in 

 order to expel carbonic acid, and to precipitate phosphates 

 and albumin. Then, drop into each tube a strip of blue 



