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Vol. 4, No. 4
ANALYTICAL EDITION
the permissible velocity The spiral gas washer can, in all cases, be employed only up to a certain maximum velocity (60 liters per hour) independent of the gas concentration. A possible relationship might be found if the height of the liquid in the spiral washer were varied; in this case, a shorter length of the liquid column should suffice for a more dilute gas. Now with increased flow velocity, the resistances of the gas washers become of less importance. When using finer glass filters (G3), a type which was not available to Rhodes and Rakestraw, this effect becomes even more apparent. I n this connection, it is worth calling to attention a paper by Bruckner ( I ) , who made use of a gas washer, pattern lola, with a glass filter G1, for the determination of minimal concentrations of ammonia in illuminating gas. As compared with previous experiments with older types of gas washers, he could increase the flow velocity up to sixty times the previous quantity (1500 liters per hour). The filling of the spiral gas washer of Greiner and Friedrichs
with glass grains, after the example of Friedrichs, proved to be impossible in the model used, because in this case the gas passed through the filter from top to bottom, and at high velocity the glass grains were blown out of the interior chamber.
ACKNOWLEDGMENT The author wishes to thank the Janaer Glaswerk Schott and Gen. for kindly placing a t his disposal the necessary apparatus and the steel cylinders containing the gas mixtures that were used.
LITERATURE CITED Bruckner, H., Gas- u. Wasserjach, 74, 121 (1931). Friedrichs, F., 2. angew. Chem., 32, 252 (1919). Friedrichs, F., Chem. Fabrik, 4, 203 (1931). Rhodes and Rakestraw, IND.ENQ. CHEM.,Anal. Ed., 3, 143 (1931). ( 5 ) Sieverts, A., and Halberstadt, S., Chem. Fabrik, 3, 201 (1930).
(1) (2) (3) (4)
RBCEIVED May 9, 1932.
Rapid Determination of Small Amounts of Magnesium in Presence of Phosphates W. E. THRUN, Valparaiso University, Valparaiso, Ind.
T
H E most commonly used micromethod for determining magnesium in biological fluids or ash consists in precipitating the magnesium as magnesium ammonium phosphate from the filtrate of a calcium determination and determining the phosphorus colorimetrically (2,6). BeEka ( 1 ) described a method based upon the formation of a lake by magnesium with Titan yellow. The method presented here does not require the time needed to perform a determination by the first method nor as many preparations as the second. It is suitable especially for laboratories in which such magnesium determinations are not a routine matter. The determination is based upon the formation of a lake by magnesium with curcurmin (3) in the presence of sodium hydroxide, and its colorimetric comparison with standards prepared simultaneously. The phosphates affect the color of the lake suspension but, if the standard solution also contains dissolved tricalcium phosphate, the color intensities are comparable and in proportion to the amount of magnesium present. Variations in the relatively large amounts of calcium phosphate added in no way affect the color intensities of the standard solution. This fact'and a difference in color shade suggests the formation of a magnesium-curcurminphosphate lake. The lake suspensions may be made more stable by the addition of starch glycerite solution (4). The removal of iron if present in too large quantities is also provided for. PROCEDURE. Pipet an aliquot of the ash solution (containing about 2 cc. of concentrated nitric or hydrochloric acid per liter) which is equivalent to 0.02 to 0.04 mg. of magnesium into a 50-cc. Nessler tube or volumetric flask. Dilute to about 40 cc., and add 2 cc. of starch glycerite solution (prepared by shaking some of the jelly with water and filtering) and 4 drops of a 1 per cent alcoholic solution of curcurmin. Since it is important that the unknown and standard solutions receive the same amount of curcurmin, this should be added with a pipet made for the purpose from a capillary tube. Mix contents thoroughly and add 5 cc. of 4 N sodium hydroxide. Mix again, dilute to mark, and mix.
One or several standard solutions are treated simultaneously in the same way. A standard solution containing 0.02 mg. of magnesium per cc. is prepared by dissolving 0.203 gram of MgS04.7HzO and 0.1 to 0.4 gram of tricalcium phosphate in water containing 2 cc. of concentrated nitric acid and diluting to one liter. In Nessler tubes distinct color intensities are distinguishable with differences of 0.01 mg. of magnesium. The color intensity is, however, less than is desirable for an instrument which allows for a depth of only 5 cm. The Nessler tubes may be used as colorimeters by varying the depth of liquid in them. The solutions are diluted so highly in order to prevent the rapid formation of a tricalcium phosphate precipitate. The lake suspensions are stable for several hours. When viewed through the Nessler tubes the suspensions appear to be slightly cloudy. If iron is present in sufficient quantity so that an appreciable colored suspension is formed upon adding the sodium hydroxide and diluting, it may be removed as follows: Titrate a separate aliquot with dilute sodium hydroxide to the neutral point of methyl red (pH 4 to 5 ) . Add the same amount of sodium hydroxide to the aliquot to be used and filter or centrifuge out the precipitate. At that pH, the magnesium phosphate is still soluble. When borates are present in excess of 0.6 mg. (as the oxide) magnesium-free blanks are affected slightly. The color intensities of blanks varying in boric oxide concentration from 1.4 to 8 mg. were the same. Two lake solutions were made up according to the directions given above containing 0.03 mg. of magnesium and 0.6 mg. of tricalcium phosphate. One of them contained in addition 6 mg. of boric oxide. The color intensities of both solutions were apparently the same. The slight effect, if any, of borates when present in larger amounts than 0.6 mg. can be eliminated in two ways. A solution containing 2 mg. of boric oxide may be added to each of the standard aliquots, or the sample aliquot may be evaporated to dryness with hydrochloric acid and methyl alcohol to remove the boric acid and the residue taken up with a
October 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
little hydrochloric acid and water and transferred to the reaction vessel. By this method a synthetic milk ash solution calculated to contain 0.54 mg. of magnesium was found by taking seven colorimeter readings in comparison with a standard containing 0.45 mg. of magnesium to contain 0.52 mg. A partially asbed food composite has 0.40 per centof magnesium by this method and 0.42 per cent by the modified method of Denis (2).
427
LITERATURE CITED (1) BeEka, Biochem. Z., 233, 118 (1931). (2) Hawk and Bergeim, 46Practical physiological 10th ed., p. 462, Blakiston, 1931. (3) Kolthoff, J. Am. Chem. Soc., 50, 395 (1928). (4) Thrun* EN(t* 2i (lg30)* (5) Youngburg and Youngburg, J.Lab. c l h Med., 1%158 (1930).
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RECEIVEDJuly 6, 1932.
The Baro-Buret 111. Application to Gas Density Determinations HAROLD SIMMONS BOOTHAND KARLS. WILLSON,Western Reserve University, Cleveland, Ohio
G
AS density determinations are of prime importance in the most accurate simple method. Errors and corrections the determination of molecular weights for the estab- due to weighing a large balloon were eliminated by first lishment of new gaseous compounds, the analysis of measuring the gas in a balloon, and then condensing it in a gaseous mixtures, the study of diffusion and viscosity, and small glass ampoule which was sealed off and weighed. The in many other investigations. A rapid! yet accurate, method tube was reopened to allow volatilization of the gas and for the easy determination of gas densities from small samples then reweighed. Although a simple U-manometer was used to measure pressure, an accuracy of 0.05 per cent is claimed would be of value. Early gas density determinations were unsuccessful owing with the possibility of 0,Ol per cent accuracy using a catheto the lack of suitable containers, pumps, and the means for tometer. By modifying this method, the pressure, volume, accurately measuring volume, pressure, and temperature. and temperature of a much smaller sample may be measWith the introduction of gas balloons and the modern vacuum ured in the baro-buret and the weight of the sample deterpumps, rapid strides have been made in the “balloon” meth- mined by adsorption and weighing in a glass tube filled with ods of density determination. Morley ( l e ) ,Rayleigh (I@, charcoal, as indicated in Figure 1. The use of the baroand Qermann (6) undoubtedly made some of the most valu- buret in gas evolution methods has previously been deable modern contributions to this method. They used bal- scribed (3). loonhi of more than a liter capacity, although some more recent BARO-BURET METHOD investigators have used smaller ones. All balloon methods, ADVANTAGES.The baro-buret is a simple instrument with however, are tedious, and present numerous difficulties because of contraction of the balloons on exhaustion and the the following distinct advantages: need of weighing globes and counter1. It is rapid and easy to use. poises. Large samples are required 2. It requires only a small sample. which are slow to reach equilibrium. 3. It may be adjusted to give optiCorrections are numerous and measmum conditions of volume and pressure (2). urements a t pressures greater than 4. It is possible to make several atmospheric are impossible because readings on the same sample. of the fragility of the balloons. 5. It requires few corrections. Of other methods for determining 6. It is accurate. gas densities by buoyancy (5, I d ) , by balancing a column of gas against The one disadvantage is that the a column of air ( I ) , or by dynamic determinations are m a d e a t room methods (9, I S ) , it may be said that temperature rather than at 0” C. i n general large volumes of the gas APPARATUS.To the baro-buret, are required, cumbersome manipuladescribed in previous articles (2, S), tory details are involved, and the there are attached by means of capilresults are not entirely s a t i s f a c lary tubing, the flat joints J and J’, tory. the manometer, the storage balloons, Volumeter methods (11, 15), in and the vacuum pump connections as which the volume of a known weight shown in Figure 1. All stopcocks are of gas is determined, generally rehollow-blown and p r o v i d e d w i t h quire large samples and give difficulty clamps to permit operating u n d e r in the m e a s u r e m e n t of pressure, pressure. Tube T permits transfer volume, and temperature. of the condensed gas from the generatMeasurements of gases in balloons, ing unit to the baro-buret, and by followed by adsorption or condensausing two such transfer tubes a t the tion in small weighing tubes, have flat joints, J and J’, p u r i f i c a t i o n been made by several workers (7, 8, of the gas within the apparatus it17) of which the recent work of Maass self may be accomplished by fracand Russell (14) probably provides FIGURE1. BARO-BURET WITH ATTACHMENTS tionation. The purified gas m a y
