October 15, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
to 500 ml. volume with distilled water; 50-ml. aliquot taken for titration. The solution was found t o be neutral to phenolphthalein, then 22.41 ml. 0.1 N iodine and 35.19 ml. 0.1 -V sodium hydroxide were added alternately in four portions of 5 and 7.5 ml., respectively, the excess of each reagent being added TTith the final portion. The iodine was run in rapidly from a buret, the alkali drop by drop with constant stirring. After a 2-minute interval 13.69 ml. of 0.1 iV hydrochloric acid were added to free the iodine combined as sodium iodate and 2.06 ml. 0.1 N thiosulfate were required to titrate the liberated iodine. It was then found that 9.07 ml. sodium hydroxide were used up in bringing the solution back t o the neutral point. Adding these volumes, we find that the following amounts of reagents were used: 22.41 ml. 0.1 iV iodine, 2.06 ml. 0.1 S thiosulfate, 44.26 ml. 0.1 N sodium hydroxide, and 13.69 ml. 0.1 N hydrochloric acid. Subtracting the thiosulfate
415
titer from the iodine titer and the acid titer from the alkaline titer, we find that 20.35 ml. 0.1 N iodine and 30.57 ml. 0.1 A' sodium hydroxide were consumed in oxidizing the xylose. Since 20 ml. 0.1 N iodine and 30 ml. 0 1 N XaOH are required for 1 millimol (or 10 cc. of 0.1 S)xylose, the amount of xylose actually present in the samp!e can be calculated as foll0n.s : IVt. of millimol b't. of sample
0.1.500 0.1600
0.1529
20.35 20.00
ml. reagent used x 100 = ml. reagent required per millimol per cent xylose
X - X 100 = 99.81 per cent xylose based on iodine
consumed
30.57
X __ X 100 = 99.96 per cent xylose based on alkali
30.00
consumed Literature Cited
(1) Slater and Acree, ISD. Esc. CHEM.,Anal. Ed., 2 , 274 11930).
Titration of Lead Salts' R. C. Wiley, P. X I . Ambrose, and A. D. Bowers UNIVERSITY OF M A R Y L A S D COLLEGE , PARK,AID.
HIS is a modification of the method published by Kiley
T
the method herein described varied from 0.5150 to 0.5177 gram. The average for ten determinations was 0.51 66 gram. For the approximate 0.1 molal lead acetate, where 0.5813 gram gallol in chloroform instead of stannous cliloride-thiocyanate. This pyrogallol-chloroform solution is l ery sensi- of lead was present. 0.5T92 to 0.5827 gram was found. The til-e to a small amount of the molybdate ion and is used as ai-erage for ten determinations n-as 0.5812 gram for the 0.1 an outside indicator on a spot plate. One drop of a 0.000005 S lead acetate; present, 0.2912 gram; average of ten results, N molybdate solution will cause a distinct brown coloration. 0.2919 gram. The method herein described may be used for the titration C o m m e n t a n d Discussion of lead salts directly or the titration of lead acetate formed When a rather concentrated lead solution is brought into by the solution of lead sulfate in the usual method of lead determination. The pyrogallol chloroform indicator, un- contact with the pyrogallol indicator, a brownish green coloralike the stannous chloride-thiocyanate indicator, may be used tion results. This is not likely to be mistaken for the color in the presence of large amounts of ammonium acetate in caused b y an excess of molybdate. It is rather an advantage, since it shows that the end point is as yet far away. SJ'hen titrating lead salts. For references t o literature and the manner of making up the concentration of the lead solution being titrated drops below 0.02 normal, this color no longer s h o w and a drop solutions the reader is referred to the earlier article. brought in contact with the indicator gives no color whatever Procedure until a n excess of molybdate is present. A brownish color The lead solution t o be titrated should contain no other is then seen. The brown color denoting the end of the reacmetals forming insoluble molybdates. It should be neutral- tion develops in the drop of aqueous liquid transferred from ized with ammonium hydroxide and any precipitated lead the beaker to the spot plate, and not in the pyrogallol-chlorohydroxide dissolved by boiling with ammonium nitrate. form solution. This latter remains colorless. After transferring the aqueous drop to the spot plate, the The solution must be boiled until neutral and titrated with standard molybdate 1%-hilehot. The end point is reached ttvo liquids should be mixed by stirring, thus facilitating forvhen a drop transferred to a spot plate containing the pyro- mation of the color. The maximum color appears about 3 or 4 seconds after stirring and is quite permanent. gallol-chloroform indicator is colored brown. If the indicator is exposed for 20 or 30 minutes on the spot I n order t o test the effectiveness of the indicator, several titrations mere made with a solution of sodium molybdate plate in contact with water, a brown coloration appears which 1 cc. of which equaled 0.009 gram of lead. This molybdate is probably due to the oxidation of the pyrogallol. The solution was prepared and standardized b y the previous molybdate appears merely to accelerate this oxidation. The indicator should be made b y pouring chloroform on method ( I ) . Three solutions of lead salts were prepared-a 0.1 molal pyrogallol and preserving in a glass-stoppered bottle. The solution of lead nitrate, 0.1 molal solution of lead acetate, and solution will keep indefinitely. Only a few minutes are rea 0.1 normal solution of lead acetate. Twenty-five cubic quired for sufficient pyrogallol to go into solution to make a centimeter portions of each were used for determination of lead suitable indicator. When a saturated solution is once obby the gravimetric method and the herein described volu- tained, i t must not be diluted with more chloroform before using, since this greatly decreases its sensitivity. metric method. A saturated solution of pyrogallol in water is only about oneResults tenth as sensitive to the molybdate ion as a saturated solution I n the approximate 0.1 molal lead nitrate solution, where of pyrogallol in chloroform. A saturated solution of pyro0.5163 gram of lead was present, the amounts of lead found by gallol in carbon tetrachloride seems to be as suitable a n indicator for the molybdate ion as the chloroform solution. 1 Received July 6, 1930. ( I ) using as the indicator a saturated solution rf pyro-
ANALYTICAL EDI T I O S
416
The solution when being tested for molybdate ion must be either neutral or slightly alkaline. It must not be very acid or the indicator loses its sensitivity. I n an acid solution the concentration of the molybdate must reach 0.002 normal before it can be det'ected. The color which forms. IiorTever, is the same as in a neutral or alkaline solution. The solution being tested must not hal-e a high coiicentration of hydroxyl ions, for the hydroxyl ion itself will cause the brown colorat'ion to appear. Ammonium salts have no effect on the indicator, nor does the precipitated lead molybdate. I n contact with a fairly concentrated solution of the molybdate ion, say 0.1 normal. the indicator shows a deep reddish brown color. Since many molybdates are insoluble, the indicator herein
1-01, 2 ,
so. 4
described should form a basis for other voluiiietric molybdate methods. I t might also form the basis for the determination of molybdenum colorimetrically. Conclusions
The results obtained by the volumetric method check very closely x i t h those obtained by the gravimetric method. but the time required is much less by the volumetric method. A saturated solution of pyrogallol in chloroform is a very sensitive indicator for the molybdate ion. An aqueous solution of pyrogallol is much less sensitive than a chloroform solution. Literature Cited (1) \Viler. IKD.EXG.CHEM, Anal. Ed., 2 , 124 (1930).
Identification of Aluminum and Magnesium in Printing Inks' Louis M . Larsen INTRRXATIONAL PRINTING1.-
ONCENTR.4TED printing inks are frequently extended with transparent inks to improve their printing qualities, and a t the same time to arrive a t a reasonable cost. The important transparent extenders are precipitated aluminum hydroxide and precipitated magnesium carbonate. Barium sulfate is also a popular extender, but it belongs to the semi-opaque type of inks. Kot only is aluminum hydroxide used as an extender, but it is often used as a substratum upon which organic dyestuffs are precipitated producing lake pigments. Furthermore, ultramarine blue, aluminum phosphate, and some aluminum lakes contain aluminum in other forms than the hydroxide. Aluminum powder itself is used as the pigment in so-called silver inks. It is obvious, therefore, that aluminum may be present in the final ink in a variety of forms, but usually as the hydroxide. Magnesium is very rarely present in inks except as the carbonate. The identification of both aluminum and magnesium involves the use of lake-forming dyestuffs, capable of detecting small quantities of the above elements in the presence of other ingredients used in inks. These dyestuffs are aluminon ( 2 , 5 ) for aluminum, and benzopurpurine 4B (1) for magnesium.
C
Preparation of Test Strips Inasinuch as nearly all of the paper manufactured today has been treated with an alum solution, a paper that is free from aluminum must be used in order that this element may be properly identified. I t is not necessary, however, t o employ a special paper for the detection of magnesium. I n order to prevent the formation of pigment suspensions and even colloidal solutions, it is advantageous to add some highly viscous linseed varnish, together with a small percentage of a concentrated cobalt drier (4 per cent cobalt) to the ink before printing. The oxidation of the linseed varnish to insoluble linoxyn keeps the pigment from floating out mechanically. The modified ink is then either printed on paper using a proof press or pulled down as evenly as possible on the paper with a steel scraper. The rate of oxidation (drying) can be increased by placing the prints in an electric o\-en at 70" C. After the prints have become dry by oxidation, they are cut 1R
CCUT July ~ 7, 19SO.
CORPORATION, SEW YORK, IY. x.
up into strips ("8 by l l / z inches) using a photo card trimmer. Each strip is marked by a pencil for identification. Procedure for Aluminum Place four dried test strips in a test tube and cover half with a 2 N solution of hydrochloric acid. Boil gently, with shaking, for 1 minute. Pour the extract into another test tube and cool, leaving the paper strips behind. If not clear, filter. Determine whether or not' iron is present before proceeding further. Dilute 1 cc. of the extract with 10 cc. of distilled water, add R few drops of a 5 per cent solution of potassium ferrocyanide solution, and shake. A distinct blue indicates the presence of appreciable amounts of iron. If there is not more than a trace of iron, as is the case in 98 per cent of the inks, continue the test for aluminum. To the clear acid extract add an equal volume of a special aluminon reagent,2 and mix well. Warm cautiously to boiling, avoiding bumping as much as possible, and boil gently for 1 minute. Allow to stand in a rack for 5 minut'es longer to promote identification of traces. h deep red flocculent precipitate indicates that aluminum is present. Absence of a precipitate indicates that aluminum is absent above minute trace (possibly 1per cext in inks). Add to the cooled solution containing the precipitate an equal yolume of a prepared alkaline aminoniuiii carbonate s ~ l u t i o n . ~If the precipitate is unchanged after thorough shaking in the cold, report, aluminum as being present in the ink. Should the solution be highly colored before or after the addition of the alkaline solution, filtration followed by washing with distilled water and later denatured alcohol will usually make it possible to inspect the color of the precipitate. If desired, the entire process of reprecipitation, etc., can be applied t,o the contaminated precipitate, yielding a purer precipitate, more suitable for observation. Procedure for Magnesium Place four dried test strips in a test tube and boil with a 5 per cent acetic acid solution for 2 minutes. Pour the acid 8 290 grams crystalline ammonium acetate, 10 grams glacial acetic acid, and 1 gram aurin tricarboxylic acid, diluted with distilled water t o a liter. 8 100 grams ammonium carbonate, 50 cc. concentrated ammonia water, 850 cc. distilled wster.
