October 15, 1931
INDUXTRIAL AND - ENGINEERING CHEiVISTRY
357
Method for Determination of Small Quantities of Paraform in Various Mixtures‘ Woltor Weinberger 1483 WALTONAYE., NEW YORK,N Y.
HIS method may also
T
A method for determining paraform in certain typii n g r e d i e n t s present would be applied to the decal mixtures is discussed, the experimental results permit such a separation. termillation of formalobtained in seeking the method given, and the method Again, paraform cannot be described in detail. dehyde in various mixtures, measured as such. Its conor to the determination in The percentage error of a determination as carried stant depolymerization, even such mixtures of any easily Out by this method is only 1 per cent. Romjin’s if very slight, would prevent method is found to be more reliable and accurate for this. T h e o n l y p o s s i b l e decomposed c o m p o u n d or the determination of formaldehyde in very dilute method Seems to be to transpolymer of formaldehyde. Commercial p a r a f o r m is solutions than any other of the well-known methods. form the paraform into formcommonly k n o w n as p a r a aldehyde, to determine the form, paraformaldehyde, and trioxymethylene. It is appar- formaldehyde, and to calculate the equivalent amount of paraently a mixture, of varying composition, of polymers of formal- form in accordance with the equation (HCHO). = n(HCH0). dehyde, each having the general formula (HCHO),. Since Paraform is broken down into formaldehyde by heat or the name “trioxymethylene” has been specifically applied steam, especially in the presence of dilute acids. Formaldeto a definite compound, (HCHO),, its use in describing such hyde, as is well known, distils with water or with steam. a mixture of polymers is misleading. Paraform is more acThese considerations suggest, as an answer to the first curately described as polyoxymethylene, or, as the author question, some sort of distillation. But for quantitative rehas done, following the suggestion of Austin M. Patterson, sults, under what conditions must we distil, and how great as polymerized formaldehyde. All quantitative results re- a volume must be distilled over? Then, these questions ferring to paraform will be expressed in this paper in terms being answered, how shall we determine the formaldehyde of formaldehyde, with the legend “formaldehyde in polymer- in the distillates, which will necessarily be very dilute soluized form.” tions? Commercial paraformaldehyde is a product which is being The total available methcds for determining formaldehyde widely used today as an antiseptic and disinfectant. It is have been tried in solutions of known formaldehyde content, generally met with as a white powder having an odor of the strengths of the solutions so used being comparable to formaldehyde. It is insoluble in ether and alcohol, sparingly those of the distillates. soluble in cold water, and soluble in solutions of the fixed The method of oxidizing formaldehyde to formic acid in alkalies, with decomposition. When heated it is partly con- accordance with the following equation verted into formaldehyde, partly sublimed unchanged. HCHO HzO 1 2 = 2HI HCOOH This compound is rarely used by itself as an antiseptic or disinfectant; but is most bften mixed with talc and alkaline and titrating the excess iodine was found to be very unreliearths to make a dusting powder or an insecticide. Because able for the determination of formaldehyde in these dilute of its increasing use, it was deemed advisable to find a rapid, solutions. The more usual peroxide-sodium hydroxide reliable, and accurate method for its determination in such method was also found to be unreliable at such dilutions. typical mixtures as paraform and talc, clays, earths, oxides Further experimental data showed that the results obtained of certain metals, borates, stearates, etc. by the bisulfite method and by the ammonia method could not be trusted where there was so much water and so little Method for Determination of Formaldehyde formaldehyde. The available methods of determining formaldehyde have The method finally accepted as being reliable, and adopted, been tried, and Romjin’s method (1, 2,s)adopted as the only was the one depending on the fact that formaldehyde forms one giving reliable results in solutions as dilute as the distillates, an additive product with cyanides, and that the cyanide so In mixtures of the type discussed, there seems to be no known used does not react with silver salts. method, and no method suggests itself, for determining paraA known weight of potassium cyanide is added to the form as such. This being so, two very obvious questions formaldehyde solution. A definite volume of standard silver present themselves: (1) how to free the paraform from the nitrate is then added. The silver cyanide formed is filtered large bulk of matter present (talc, etc.) and from any other off and the excess silver is determined in accordance with the foreign material which may interfere with the determina- following equations: tion; and (2) having freed the paraform from interfering subKCN AgN03 = AgCN+KNOa stances, how to determine its amount. KCN+HCHO = KCNHCHO I n freeing the paraform from the large bulk of matter, it AgN03 + KCNHCHO = KCNHCHO AgNO3 (excess) ( 1 ) must be remembered that we are dealing with a polymer of Experiments formaldehyde, which under ordinary conditions is prone to depolymerization, so that some formaldehyde must always A sample of paraform containing 97 per cent formaldehyde be present. Therefore, all considerations which attach to in polymerized form, when assayed in accordance with the the determination of small amounts of formaldehyde will also method in the U. S. Pharmacopeia, 10th ed., page 277, was apply here. For instance, we cannot attempt to dissolve out obtained. the polymer with some suitable solvent, filter, evaporate, and Typical dusting powder mixtures (talc, alkaline earths, weigh. Such a method is clearly unsuitable, even if the inert stearates, clay, borates, etc.) containing definite and known amounts of this paraform were prepared. 1 Received September 8 1930 ~~
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ANALYTICAL EDITION
358
After trials of a number of types of distillation, the use of steam distillation was decided upon as the type which could be used with the utmost simplicity, neatness, and economy of time. When the ordinary distillation was attempted, the foaming was so uncontrollable as to require constant watching. Typical experiments and some of the experimental results obtained are as follows: (1) Twenty grams of a freshly prepared mixture, accurately weighed, were transferred to an 800-ml. distilling flask; 25 ml. of water plus 10 ml. of dilute sulfuric acid were added. The contents of the flask were then steam-distilled so that about 110 drops distilled over each minute, the volume in the flask being kept nearly constant. Various fractions of the distillate were collected, by definite volumes, in volumetric flasks. The formaldehyde in each fraction was determined in accordance with the cyanide method as sketched above, and given in detail after the conclusion. Qualitative tests for the presence of formaldehyde in each fraction were also made. For this purpose Schiff's reagent was used. In place of listing each distillation separately, the results of a typical set of distillations is arranged in Table I. All distillations were run on freshly prepared samples. Table I-Typical S e t of Distillations (Charge contains 0.0210 gram of formaldehyde in polymerized form) COLOR TESTWITH FORMALDEHYDE FOUNDIN DISTILLATE SCHIFF'S REAGENT 2 3 4 5 6 A v . 1st 50ml. 2nd50 ml. 3rd 50 ml.
4th 5th 6th 7th 8th
60 ml. 50 ml. 50 ml. 50 mi. 50 mi.
Total Error
%
%
%
%
%
%
48 24 3 12.8
49 25 13 7 4 2
50 24 12 6 3 3
47 26 14 6 3 3
48 25 13 7 4 4
48 25 13 7 4 3 0
99 -1
101 $1
6.7
4.3 2.4
0.5 .. .. -.. .. . .. .. .. .. .. ,
99.0 -1
100 0
98 -2
Deep Deep Moderate Less Weak Perceptible Traces No color
Vol. 3, No. 4
in mind that the distillation was studied -within limited range. Transfer 20 grams of the sample to an 800-ml. Kjeldahl flask. Add 25 ml. of water and 10 ml. of dilute sulfuric acid. Add paraffin to prevent foaming. Steam-distil rapidly (about 110 drops per minute, keeping the volume in the distilling flask fairly constant), catching the first 300 ml., or 200 ml. if extreme accuracy is not desired, in a volumetric flask. Into each of two 50-ml. volumetric flasks run, accurately, 9 ml. of 0.1 N silver nitrate. Add 6 drops of concentrated nitric acid. To one of the flasks add an excess of potassium cyanide solution. A 0.1 N solution is easiest. Make up to the mark with water, shake, and filter. Pipet 25 ml. of the filtrate into a flask, add 5 ml. of ferric alum indicator, and titrate the excess silver nitrate with standard thiocyanate solution. This serves as a control. Pipet 25 ml. of the distillate into a small beaker. Add the same amount of cyanide solution that was added to the control, and stir well. Transfer this solution to the other small volumetric flask, make up to the mark with water, shake, and filter Pipet 25 ml. of this filtrate into a flask, add 5 ml. of ferric alum indicator, and titrate the excess of silver nitrate with the standard thiocyanate solution. The per cent of formaldehyde in polymerized form is as follows:
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If 300 ml. have been distilled, (ml. KCNS for sample ml. for control) X normality of KCNS X 3 6 If 200 ml. have been distilled, (ml KCNS for sample ml. for control) X normality of KCNS X 2 6
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The charge taken and the aliquots used, as well as the amount of the cyanides and the strengths of the standard solutions, all depend, of course, on the amount of formaldehyde present. Literature Cited (1) Assocn. Official Agr. Chem., J . Assocn. O f i C Z d ~Agr. Chem , 8, 67 (1925). (2) Romjin, 2. anal. Chem., 36, 18 (1897). (3) U. S. Dept. Agr., Bur. Chem, Bull. 132,49 (1910).
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( 2 ) This work was repeated with several different mixtures and identical results were obtained. It must be remembered, of course, that the volume of liquid in the distilling flask and the rate of distillation were both kept very much the same for each distillation. (3) Charges were varied so that it was necessary to distil amounts of formaldehyde ranging from 0.02 gram to 0.20 gram. In all cases similar results were obtained for each set of distillations in that the formaldehyde was practically completely carried over in 300 ml. (4) Fprmaldehyde was added to the contents of the flask and distilled. One hundred per cent recovery was obtained, but determinations were made only within the range indicated ,in paragraph 3 above.
From a study and consideration of the foregoing results the following conclusions must be drawn: (1) Within the range studied, practically all of the formaldehyde present is in the first 300 ml. distilled over. (2) All but 5 to 10 per cent of the formaldehyde present is in the first 200 ml. distilled over. Therefore, for most purposes, and since the formaldehyde content of many commercial products is so small, it is sufficient to distil over only 200 nil. (3) The error of 1 per cent is probably an error inherent in the manipulations. Method for Determination of Paraform This method, or the operative details of it, is based on the results of the trial distillations and the conclusions drawn therefrom. It has been used for the determination of paraform in many different mixtures and has been found reliable and accurate. In performing this distillation, certain theoretical considerations endemic t o every steam distillation must be remembered. If the same percentage of formaldehyde is to be found in the same volume of distillate, the volume of liquid in the distilling flask and the rate of distillation as indicated here must be adhered to. It should also be kept
A Dish for Toxicity Tests' A. S . Daniels SOUTHERN PACIFICLINES,HOUSTON, TEXAS
T HAS been pointed out that in testing the toxic properties Ifactory of certain wood preservatives, the Petri dish is not satisas it may permit the volatilization of 9pme of the substance under test ( I ) . Schmitz (2) has recommended placing the inoculated Petri dishes under small bell jars set on glass plates. Bateman and Henningsen ( I ) suggest glass-stoppered Erlenmeyer flasks in place of Petri dishes. Both of these methods have serious disadvantages, particularly when incubator space is limited. The writer has found that the use of Stender dishes offers distinct advantages over any of the methods suggested. Cultures are plated and inoculated in Petri dishes in the usual way. A sterile 100-mm. Stender dish is then inverted on the table. The bottom is raised a few inches and the prepared Petri dish slid on to the Stender dish cover. The cover of the Petri dish is removed, the ground groove in the Stender dish cover is filled with melted hard vaseline, and the Stender dish gently lowered and fitted back in to the Vaseline-filled groove of the cover. 1 Cultures so prepared can be stacked up to the capacity of the incubator, they are readily available for observation, and they effectually prevent the volatilization of any appreciable portion of the substance under test. Literature Cited (1) Bateman and Henningsen. Proc. A m . Wood-Preservers' Assocn., 19, 136 (1923). (2) Schmitz, IND. ENG. CHEM.~ Anal. E d , 1, 76 (1929). 1
Received May 29, 1931.
