- 48 — 
in view of the low citral- content of lemon oil this difference is very- 
marked and renders the practical utility of the process very doubtful. 
In the lemon oil examined, a citral-content of 4 to 4,5% was determined. 
Determinations recently again made by us by Berte's and also by 
Kremers' method with mixtures of known citral-content led to no 
better result than our previous experiments; for this reason we are 
still sceptical about such a process for the estimation of citral in lemon 
oil. We are all the more doubtful about the reliability of the method, 
as, in view of the low citral-content of lemon oils, added to the small 
quantity of only 5 cc oil employed, the possibility of errors appears 
altogether too great. 
Now Sad tier has recently recommended a method of estimating 
the aldehyde^), which is based upon the fact observed by Tiemann, 
that when citral is shaken with a neutral solution of sodium sulphite, 
citral dihydrosulphonic acid is formed with simultaneous splitting off of 
sodium hydrate: 
C9H,5CHO + 2Na2S03 + 2H20 = C^H,, (S03Na)2CHO + 2NaOH. 
By titrating with semi-normal hydrochloric acid the quantity of 
liberated sodium hydroxide is determined, and from this the citral- 
content calculated. The process is carried out as follows: 
5 to 10 gm. lemon oil in an Erlenmeyer flask, after neutralising 
the free acid with semi-normal potash liquor, are mixed with 5 times 
the quantity of a 20^/q solution of sodium sulphite which has previously 
been neutralised, at the temperature of the water-bath, with semi-normal 
hydrochloric acid, whereby rosolic acid is used as indicator. The mix- 
ture is heated in the boiling water-bath, with frequent shaking, and the 
sodium hydroxide formed during the reaction is from time neutralised 
with semi-normal hydrochloric acid. The reaction is completed as soon 
as the solution remains neutral, which is the case in about half an hour. 
From the quantity of hydrochloric acid used up, the quantity of liberated 
sodium hydroxide is ascertained, and from this the citral-content. If a 
represents the number of cc semi -normal acid consumed, and s the 
quantity of oil employed, in grams, the percentage of citral is calculated 
by means of the following formula: 
s 
Sad tier mentions in his work only four analyses by way of evi- 
dence; Kremers and Bran del have made a whole number of 
determinations in putting this method to the test. In every case the 
result obtained was most satisfactory; in 16 determinations the extreme 
difference was only once as high as 0,8%, but generally the difference 
observed did not exceed 0,3 
^) Americ. Journ. Pharm. 76 (1904), 84. 
