New YorK AGRICULTURAL EXPERIMENT STATION. 339 
In making standard solutions, pure distilled water should 
be used if possible, or else as pure rain-water as can be 
obtained. 
Instead of purchasing the solid sodium hydroxid one can 
obtain a normal solution of the alkali directly from chemical 
supply-houses and then dilute this in the manner already 
indicated. 
Solutions of sodium hydroxid, when exposed to the air, ab- 
sorb carbon dioxid and change in strength so as to become 
unreliable; they should, therefore, be kept carefully in tightly- 
stoppered bottles. 
(2) Acetic acid. This solution is made so that a given 
amount of it will exactly. neutralize the same amount of the 
standard alkali solution of the strength above indicated. The 
simplest, but not the cheapest, way of preparing this solution 
is to purchase a normal solution and dilute 1,000 cc. of this 
tOeL. 20 CCu( OL /79p: Ce, to 1,000, cc.) 
The following method of preparing standardized acetic acid 
is the one commonly used in laboratories: Concentrated acetic 
acid, 99 per ct. or more pure, is employed. In preparing con- 
siderable amounts, one measures out about 12 cc. and dilutes 
to 2 liters of stock solution with pure, soft water (preferably, 
distilled). This makes a solution approximately tenth-normal, 
but somewhat too strong. One takes 25 cc. of this solution, 
adds two or three drops of phenolphthalein solution and then 
runs in from a burette the standardized alkali until the neutral 
point is reached, when the solution becomes faintly but dis- 
tinctly pink in color, the coloration remaining for some time. 
The amount of alkali solution thus required is read from the 
burette. Suppose, for example, that 25 cc. of the diluted acetic 
acid requires 27.5 cc. of alkali. This means that each 25 ce. of 
acid should be diluted to 27.5 cc. in order to have the proper 
strength, or each 1,000 cc. of acid solution should be diluted 
to 1,100 cc. by addition of 100cc. of water. The method of 
calculation, expressed as a general rule, may be stated as 
follows: To find the amount of standard acid, multiply the 
