NOTES.
(1) It is important that the concentration of acid in the oxidation mixture and the time of oxidation should be strictly adhered to.
(2) Before the bichromate is added to the glycerine solution it is essential that the slight excess of lead be precipitated with sulphuric acid, as stipulated.
(3) For crudes practically free from chlorides the quantity of silver carbonate may be reduced to one-fifth and the basic lead acetate to 0.5 cc.
(4) It is sometimes advisable to add a little potassium sulphate to insure a clear filtrate.