(_E_) _Subacetate of Lead._--Boil a 10 per cent. solution of pure lead acetate with an excess of litharge for one hour, keeping the volume constant, and filter while hot. Disregard any precipitate which subsequently forms. Preserve out of contact with carbon dioxide.

(_F_) _Pota.s.sium Ferricyanide._--A very dilute, freshly prepared solution containing about 0.1 per cent.

THE METHOD.

Weigh 20 grams of the glycerine, dilute to 250 cc. and take 25 cc. Add the silver carbonate, allow to stand, with occasional agitation, for about 10 minutes, and add a slight excess (about 5 cc. in most cases) of the basic lead acetate (_E_), allow to stand a few minutes, dilute with distilled water to 100 cc., and then add 0.15 cc. to compensate for the volume of the precipitate, mix thoroughly, filter through an air-dry filter into a suitable narrow-mouthed vessel, rejecting the first 10 cc., and return the filtrate if not clear and bright. Test a portion of the filtrate with a little basic lead acetate, which should produce no further precipitate (in the great majority of cases 5 cc. are ample, but occasionally a crude will be found requiring more, and in this case another aliquot of 25 cc. of the dilute glycerine should be taken and purified with 6 cc. of the basic acetate). Care must be taken to avoid a marked excess of basic acetate.

Measure off 25 cc. of the clear filtrate into a flask or beaker (previously cleaned with pota.s.sium bichromate and sulphuric acid). Add 12 drops of sulphuric acid (1: 4) to precipitate the small excess of lead as sulphate. Add 3.7282 grams of the powdered pota.s.sium bichromate (_A_). Rinse down the bichromate with 25 cc. of water and let stand with occasional shaking until all the bichromate is dissolved (no reduction will take place in the cold).

Now add 50 cc. of 50 per cent. sulphuric acid (by volume) and immerse the vessel in boiling water for two hours and keep protected from dust and organic vapors, such as alcohol, till the t.i.tration is completed.

Add from a weighing bottle a slight excess of the ferrous ammonium sulphate (_C_), making spot tests on a porcelain plate with the pota.s.sium ferricyanide (_F_). t.i.trate back with the dilute bichromate.

From the amount of bichromate reduced calculate the percentage of glycerol.

1 gram glycerol = 7.4564 grams bichromate.

1 gram bichromate = 0.13411 gram glycerol.

The percentage of glycerol obtained above includes any oxidizable impurities present after the purification. A correction for the non-volatile impurities may be made by running a bichromate test on the residue at 160 C.

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 quant.i.ty 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 pota.s.sium sulphate to insure a clear filtrate.

SAMPLING CRUDE GLYCERINE.

The usual method of sampling crude glycerine hitherto has been by means of a gla.s.s tube, which is slowly lowered into the drum with the object of taking as nearly as possible a vertical section of the glycerine contained in the drum. This method has been found unsatisfactory, owing to the fact that in cold climates glycerine runs into the tube very slowly, so that, owing to the time occupied, it is impossible to take a complete section of the crude. Another objection to the gla.s.s tube is that it fails to take anything approaching a correct proportion of any settled salt contained in the drum.

The sampler which is ill.u.s.trated herewith has been devised with the object of overcoming the objections to the gla.s.s tube as far as possible. It consists of two bra.s.s tubes, one fitting closely inside the other. A number of ports are cut out in each tube in such a way that when the ports are opened a continuous slot is formed which enables a complete section to be taken throughout the entire length of the drum.

By this arrangement the glycerine fills into the sampler almost instantaneously. There are a number of ports cut at the bottom of the sampler which render it possible to take a proportion of the salt at the bottom of the drum. The instrument is so constructed that all the ports, including the bottom ones, can be closed simultaneously by the simple action of turning the handle at the top; a pointer is arranged which indicates on a dial when the sampler is open or closed. In samplers of larger section (1 in.) it is possible to arrange a third motion whereby the bottom ports only are open for emptying, but in samplers of smaller dimensions (5/8 in.) this third motion must be dispensed with, otherwise the dimensions of the ports have to be so small that the sampler would not be efficient.

In using the sampler it is introduced into the drum with the ports closed, and when it has touched the bottom, the ports are opened for a second or two, then closed and withdrawn, and the sample discharged into the receiving vessel by opening the ports. When the drum contains salt which has deposited, the ports must be opened before the sampler is pushed through the salt, thus enabling a portion to be included in the sample. It is, however, almost impossible to obtain a correct proportion of salt after it has settled in the drum and it is therefore recommended that the drum be sampled before any salt has deposited. A sampler 1 in.

in diameter withdraws approximately 10 oz. from a 110-gal. drum. A sampler 5/8 in. in diameter will withdraw about 5 oz.

FOOTNOTES:

[13] Zeit. Angew. Chem. 19, 385 (1906).

[14] Zeit. Angew. Chem. 27, 11-20 (1914).

[15] Bull. 107, Bur. Chem. U. S. Dept. Agriculture.

[16] Richards and Gies, Am. J. Physiol. (1902) 7, 129.

[17] Seifensieder Ztg. (1913) No. 46.

[18] Bull 107, Bur. Chem. U. S. Dept. Agriculture.

[19] Carbon is readily burned off completely, without loss of chlorides, in a gas-heated m.u.f.fle furnace adjusted to a dull red heat.

[20] An electric oven suitable for this work, which is readily adjusted to 160 degs. C., has been made for Mr. Low and the chairman, by the Apparatus and Specialty Company, Lansing, Mich. Its size is 9-1/2 10 16 inches, and capacity 8 Petrie dishes. It gives a strong draft at constant temperature.

[21] A precipitate at this point is an indication of the presence of iron or alumina, and high results will be obtained unless a correction is made as described below.

CHAPTER VII

Standard Methods for the Sampling and a.n.a.lysis of Commercial Fats and Oils[22]

The following report of the _Committee on a.n.a.lysis of Commercial Fats and Oils_ of the _Division of Industrial Chemists and Chemical Engineers_ of the American Chemical Society was adopted April 14, 1919, by unanimous vote:

W. D. RICHARDSON, _Chairman_, Swift and Co., Chicago, Ill.

R. W. BAILEY, Stillwell and Gladding, New York City.

W. J. GASCOYNE, W. J. Gascoyne and Co., Baltimore, Md.

I. KATZ,[A]

Wilson and Co., Chicago, Ill.

A. LOWENSTEIN,[A]

Morris and Co., Chicago, Ill.

H. J. MORRISON, Proctor and Gamble Co., Ivorydale, Ohio.

J. R. POWELL, Armour Soap Works, Chicago, Ill.

R. J. QUINN,[A]

Midland Chemical Co., Argo, Ill.

PAUL RUDNICK, Armour and Co., Chicago, Ill.

L. M. TOLMAN, Wilson and Co., Chicago, Ill.

E. TWITCh.e.l.l,[A]

Emery Candle Co., Cincinnati, Ohio.