15 



the last of the light pink color. This work should be repeated until 

 accuracy is assured. The following- is an example of results : 



1st. 10 c.c. of alkali required 11.5 c.c. of acid for neutralization. 



2nd. 10 c.c of alkali required 11.45 c.c of acid for neutralization. 



3rd. 10 c.c. of alkali required 11.5 c.c. of acid for leutralization. 



In this case, we would accept 10 to 11.5 as the relative strength 

 of the two solutions. The alkali is, therefore, the stronger, and must be 

 diluted. If 1.5 c.c. of water be added to 10 c.c. of the alkali solution, 

 1 c.c. of the alkali ought exactly to neutralize 1 cc. of the acid. There- 

 fore, for every 10 c.c. of the alkali solution add 1.5 c.c. of water. Meas- 

 ure out the amount of the solution and pour into a clean dry bottle. Cal- 

 culate the amount of water required to dilute the alkali to the proper 

 strength, and add it to the contents of the bottle. Mix well, and test 

 correctness of work by proving that 10 c.c. of the one solution will 

 exactly neutralize 10 c.c. of the other. If it does this, the solution is 

 correct. 



Testing the Acidity of Milk or Cream. I^y means of a pipette 

 (a 10 c.c is a convenient size) measure out a definite quantity of the milk 

 or cream to be tested and deliver into a beaker or cup. If distilled or 

 rain water is handy rinse out a pipette once, and add the rinsings to the 

 sample. Dilute with 50 c.c. of water, and add three or four drops of 

 thi- indicator. Now, having the alkaline solution in the burette, carefully 

 note the point at which the surface or the liquid .'^'.ands in the burette and 

 then cautiously let it drop into tr.e milk or cream bein^.; tested. Keep 

 the sample well stirred while adding the alkali. The acid in the sample 

 will gradually be neutralized by the alkali added, until at last -a uniform 

 pink color appears, which will sovvlv fade avvav. Hie most delicate 

 point is the first change to the uni''crp: pink color, which the sample shows 

 when the acid contained therein has been just neutralized. Because of 

 tho influence of carbonic acid oi t'-'e atmc^ohe'e the pinic color is not ptr- 

 mancnt unless a slight excess of alkaM solution has bee-i added. The 

 operator should not, therefore, be led to believe by the disappearance of 

 the color after a short time, that the neutral point has not been reached. 

 Havinp decided on the neutral poi.it, a^caln u)iu\ i he buret t.f at the surface 

 of the liquid, and the difference between this readin.r and the first is the 

 amount of alkali solution used to neuralize the acid in the sample taken. 



The calculation of the per cent, of acid is simple. The alkahne 

 solution used is of such a strength that when a 10 c.c. pipette is used, 

 the number of cubic centimeters of alkaline .solution required to neutralize 

 the acid in the milk or cream has simply to be multiplied by O-l- Thus, 

 if .5.6 cubic centimeters of the alkali be used then 0.6x0.1- .ob per 



cent. acid. . , , 



To insure accuracy the utmost care and cleanlmess must be observ- 

 ed in everv detail of the work. All water used with the m.lk .or cream or 

 in makin- the alkaline solution should be either distilled or pure rain 

 water. The burette and pipette, after being wa.shed, must be rinsed 

 out two or three times with the solution they are intended to measure. 

 The knowledge the operator may gain from such tests will not only 



