T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y . July, 1909
476
where extreme accuracy is desired, this pycnometer is also suited for determinations of non-volatile oils, especially those of too high viscosity for use with the Westphal balance or hydrometer. The pycnometer, as shown in Fig. I , consists of a fairly heavy, straight-walled glass tube, 7 0 mm. long and 2 2 mm. diameter ground to receive a solid glass stopper with a 1.6 mm. bore in place of the usual capillary opening. The lower part of this stopper is made concave in order t o allow all air bubbles to escape through the bore. The depth of the cupshaped depression is 4.8 mm. at the center. The stoppered tube has a capacity of about 24 cc. and when empty weighs about 28 grams. Its principal advantages are t h a t ( I ) any desired amount of bitumen may be poured in without touching the sides above the level desired; ( 2 ) i t is easily cleaned; (3) on account of the 1/16’’ bore the stopper can be more easily inserted when the tube is filled R-ith a very viscous oil, than if i t Contained a capillary opening. When working with semi-solid bitumens which are too soft to break and handle in fragments, the following method of determining their specific gravity has been employed by the writer with good results. The clean, dry pycnometer is first weighed empty and this weight called “a”. It is then filled with freshly distilled water at 25O C. in the usual manner, the weight again taken and called “b.” The bitumen should be brought to a fluid condition by the gentle application of heat, care being taken that no loss by evaporation occurs. When sufficiently fluid enough is poured into the pycnometer to about half fill it, without allowing the
FLG. A material to touch the sides of the tube above the desired level. If the presence of air bubbles is suspected, the tube may then be placed for a few minutes i n a vacuum chamber made by inverting a large glass funnel on a ground-glass plate, as shown in Fig. 2 , the edge of the funnel being smeared with desiccator grease. After all air bubbles have thus been removed, the tube and contents are cooled to 25’ C. in any suitable manner and weighed with the stopper. This weight Distilled water a t 25O C. is then poured in is called “ c . ” until the pycnometer is full, the stopper inserted and the From the whole weighed. This weight is called “d.”
weights obtained, the specific gravity of the bitumen may be readily calculated from the following formula: Specific gravity, 25O C./zjo C. = c - a/(b-a) - (d-c) Check results obtained according to the above method are accurate to within two units i n the third decimal place a s compared with the open-tube method commonly employed which is accurate t o the second decimal place only, The specific gravity of fluid bitumens may be determined in the ordinary manner with this pycnometer by completely filling i t with the material and dividing the weight of the bitumen thus obtained by t h a t of the same volume of water. The pycnometer may be readily cleaned by placing i t in a hot-air bath until the bitumen is sufficiently fluid to pour. As much is drained out as possible and the interior swabbed with a piece of cotton waste. It is then rinsed clean with a little carbon bisulphide. PREVOST HUBBARD. LABORATORY, OFFICE OF PUBLIC ROADS, U. S. DEPARTMENT OF AGRICULTQRB.
THE DETERMINATION ON ZINC BY WEIGHING AS SULPHATE. This method is similar to the determination of cadmium, manganese, cobalt, magnesium and calcium as sulphate. It has been in use by one of the writers for some years and has given perfectly satisfactory results. The zinc is precipitated customarily as sulphide from a hot solution slightly acid with sulphuric or hydrochloric acid, to which ammonia is added during precipitation until the solution is but faintly acid. Precipitation made in this way is complete and the precipitate is readily filtered and requires washing with hot water only.’ As will be shown presently, removal of all traces of ammonium salts is not necessary. The zinc sulphide is washed into a deep beaker with as little water as possible and dissolved in hydrochloric acid which has trickled through the filter paper in order to take up any sulphide still adhering, To avoid effervescence during subsequent evaporation the solution i n the covered beaker is boiled until hydrogen sulphide is completely expelled ; i t is then transferred to a weighed porcelain crucible and evaporated on the water bath after addition of only a little more than the quantity of sulphuric acid necessary to form zinc sulphate. When no further evaporation takes place, the crucible is placed in a sniall air bath, either a Hillebrand radiator2 or a large porcelain crucible fitted with asbestos ring a s described b y Treadwell.* The excess of sulphuric acid having been removed by heating in such an air bath, the crucible is cautiously subjected to the direct heat of the Bunsen flame and finally heated t o redness for several minutes. The crucible with zinc sulphate is colored in the desiccator and weighed. The results are as a rule accurate to within one or twotenths of one per cent. A solution of zinc chloride was made by dissolving J. T. Baker’s chemically pure “analyzed” zinc in hydrochloric acid and diluting so t h a t 50 cc. of solution contained 0.3005 gram zinc. In measured volumes of this solution the zinc 1 See Waring, “ O n Precipitation from Formic Acid Solution.” l o w . A m . Chem. SOC.. 26,27 (1904). * Bulletin 305, United States Geological Survey. page 29. 8 “Quantitative Analyse.” fourth edition, page 24.
NOTES i l N D CORRESPONDENCE. was determined as sulphate and, for comparison, as pyrophosphate by the method given by iyaring.' I n these determinations the solution for analysis was measured out by one of the writers and the determination made by the other, so t h a t the analyst had no knowledge of the result which he was expected to get. TABLEI. DETERMINATIOIS O F ZINC
AS SULPH.4TE
A N D PYROPHOSPHATE,
0.3043 g. zinc. 0.1541 0.0909 0.2428 As pyrophosphate. 0.2861 g. zinc. 0.1656 0.2224
furnishes increased surface for filtering but also allows the denser part of the precipitate to settle in a ring a t the bottom of the crucible, leaving the asbestos on the apex of the filter in such a condition that the filtrate and washing liquids can be quickly and completely removed. B. hfE.4RS. UNIVERSITYO F ILLINOIS, b f A Y 31, 1909
WITH
CALCULATEDRESULTS. Found. -4s sulphate.
477
Calculated. 0.3035 g. zinc. 0.1533 0.0909 0.2425
THE DETERMINATION OF OXIDES OF IRON AND ALUMINA IN FLORIDA PHOSPHATES.
The method as given below is a modification of the old Glaser method, and can be depended upon to give excellent results in all except the few instances in which manganese occurs in any appreciable quantity. It must also be noted 0.2854 g. zinc. that this method does not include any iron or alumina present 0.1656 in the shape of pyrite, or as a silicate insoluble in acid. 0.2223 TVith reasonable care in the various operations, the results T o determine whether or not the presence of small quan- on the identical pulverized sample should not differ more tities of ammonium chloride affects the result, either by than 0.05 per cent. and are generally well within this limit. remaining unvolatilized a s sulphate or by causing volatiliza- The most important points appear to be the proper elimination of zinc chloride, zinc chloride solutions were evaporated tion of fluorine, and the use of vel.? hot water in washing the with sulphuric acid and a few milligrams of ammonium chloprecipitate. As carried out in this laboratory, the operations ride. The outcome of these experiments (Table 11) makes are as follows: i t clear that for this determination it is not necessary to One gram of the powdered sample is carefully weighed wash precipitated zinc sulphide perfectly free from ammonium out and placed in a tall beaker of about 300 cc. capacity chloride which may contaminate it. It should be added, Ten cc. of strong muriatic acid are added, and after covering however, t h a t larger quantities of ammonium chloride ( IOO with a watch glass, the beaker is placed on a gauze and quickly nig. and over) cause low results. brought to a boil. Leave on the gauze for ten minutes, TABLE11. regulating the flame so that it does not go dry, and the bulk INFLUENCE O F AJ.IMONIUM C H W R I D E O N DETER~IINATION O F Z I N C AS of the solution a t the end of the ten minutes is about 5-7 cc. SULPHATE. Let cool, and carefully decant as completely as possible into Found. Calculated. a Jena glass volumetric flask of IOO cc. capacity. Try to 0.1803 g. zinc. 0.1803 g. zinc. get all the solution to run into the flask, excepting the last 0.1804 0.1804 EUGENEC. SULLIVAN, drop or so. Rinse this last drop into the flask with the least possible amount of water. It is possible to do this with a 1%'. C. TAYLOR. little practice, without disturbing the bulk of the sand, CORNINGGLASSWORKS, CORNING,X. Y . which remains (most of it) in the original beaker. You now have about IO-IZ cc. solution in the little volumetric flask. To this solution in the flask you add 10cc. of dilute sulphuric THE PREPARATION OF GOOCH CRUCIBLES FOR acid (one-half acid of 1.84sp. gr., and half water). ASPHALT ANALYSIS. The addition of this acid will form a curdy, bulky precipiThe filtration of tarry or asphaltic precipitates suspended tate of impure sulphate of lime. Shake up the flask to mix in organic solvents on porcelain Gooch crucibles is a tedious this precipitate, and then place the flask on a gauze over and unsatisfactory process at best. The following simple Bunsen in the hood, and boil for a t least ten minutes. deviation from the ordinary method of preparing such I t may require a little practice to get the flame just right, crucibles has proven itself of value in several hundred deterto get the flask and contents t o boil hard vithout bumping minations carried out in this laboratory. off the stand-but i t is most important that the contents should boil, This boiling gets rid of nearly all the fluorine, CRUCIBLE and changes the bulky precipitate of calcium sulphate into ASBESTOS a dense, crystalline compound, which filters and washes easily. My experience has been t h a t a gauze and Bunsen pf. COWP are better than hot plate or sand bath for this particular operation, a s a quick heat gets the solution to a temperature TARRY where the violent pumping (caused by the occasional liberation of a large bubble of vapor) is avoided by causing the evolution of steam, etc., to be so rapid as to form a more A thimble-shaped cone of platinum gauze is placed in the continuous stream. bottom of a Gooch crucible and the asbestos sucked dry over After ten minutes' boiling, take the flask off the fire and i t as shown in the accompanying cut. In cases where i t is let cool to room temperature. not necessary to ignite the precipitate, fine copper gauze To go back to the beaker in which the original solution has proven itself satisfactory. I n use, the cone not only was made, it is possible t h a t the grains of sand and insoluble 1 Jour. of the Amer. C h m . S o c . , 26. 28 (1904). matter might not have been rinsed quite clean in transferring to
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