I N D U S T R I A L A S D EAYGIAI-EERINGCHE.UISTRY
May, 1923
this higher ratio when dealing with a linter with high SaOHsoluble. This is reasonable since it is known that the SaOHsoluble portion of linters is low in viscosity. The cuprammonia viscosity is lowered by the presence of the SaOH-
517
soluble portion to a much greater degree than the nitrocellulose viscosity, because a large portion of the KaOH-soluble part of the lint dissolves during nitration and purification of the nitrocelldobe.
Apparatus for Determining the Specific Gravity of Aggregates' By F. H. Tucker B U R E A U OF
ENTOMOLOGY, T . 4 L L U L A H , LA
A n apparatus has been developed by which the specific gravity of aggregates separated from bituminous mixtures can be determined, without separation into grades, to a n accuracy of 2 per cent and better. I t is adaptable to the gravity determination of fine materials, as Portland cement and sand, comparing favorably with the LeChatelier flask in results obtained, and requiring one-third as much time per determination. Although it has not been used for the apparent gravity of porous materials, there is nothing in its construction or operation t h a t would prohibit its use in the same way as any apparatus used for t h a t purpose. The essential features of the apparatus are (1) the special overflow tube, which produces a sharp cut-off of the overflowing liquid and responds to as small a n increase in
volume as 20 cc. or less; (2) the special lid and funnel combined, which effectually reduces flotation of fine material by introduction beneath the surface of the liquid, and prohibits air inclusions and splashing by providing for the spreading of the material and control of the speed a t which the material enters the liquid; (3) the glass jar, which permits the observation of behavior of the material in the liquid and is very easily and quickly cleaned. For aggregates abstractly considered, absorption, adsorption, and relative solution, are problems for investigation. The unoccupiable pore space in the aggregate material is constant for both the compressed bituminous mix and the aggregate after separation, and affects their respective densities in proportion to the relative percentages by weight.
COSTEJIPLATED study of compressed bituminous road materials involved the specific gravity determination of aggregates separated by extraction in order to determine the theoretical maximum or voidless density of bitumincius mixtures. A search of the literature and examination of laboratory practice revealed the need of an apparatus adaptable to the gravity determination of such aggregate?. Acccirding to the type of mix, aggregate. vary in size of particle from that passing a 200-mesh sieve to that retained on a 4.4-cm. (1.i5-inch) mesh. Common practice is to separate the coarse from the fine material and separately det'ermine the grayities by use of apparatus adaptable to the grades. It is highly desirable to eliminate this waste of time and increased chance for error by a single grayity determination of the aggregate as a whole.
tion between apparent and true specific gravity is dependent upon the absorption factor of the material and that i t is not practical to determine the apgarent gravity of fragments smaller than 0.5 inch diameter by any of the methods studied. For larger materials the Goldbeck, Chapman wire basket, and HubbardJackson methods were found to be equally reliable. The Bureau of Standards' modification of the LeChatelier apparatus was pronounced more convenient and rapid than the Jackson apparatus for fine materials with diameters less than 0.5 inch. Rea' described a method depending on the difference in specific gravity and the nonmiscihility of water and kerosene, to measure the displaced volume of the aggregate, including any pores that the particles may contain.
A
History Buckly' pointed out the faulty practice in the methods for specific gravity determinations of building stone, and recommends a procedure for determining porosity. Thorner3 proposed a method for determining the pore space in building materials, determining the true specific gravity by a Schumaunschen apparatus, and the apparent specific gravity by a device designed by himself, which is essentially a glass jar fitted with a ground-glass top containing an overflow tube and a vertical measuring tube connected to a tube sealed into the lower part of the wall of the jar. Seger and Gramendemployed the Thorner principle, but simplified the apparatus and procedure. Hilleh a n d 5 has a noteworthy discussion pertaining to the importance of correction for absorption by porous materials in the specific gravity determination of rocks. Hubbard and Jackson,6 after a comparative study of seven methods for the specific gravity determination of aggregates, concluded that an appreciable variaI 2 J
4
5
Received August 4 , 1924. K i s . Geol. S a t . H i s f S u r u e y Auli. 4, 63, 70 (1895) Chern. Ztg., 29, 744 (1905). I b i d . , 29, 884 (1905). U . S . Geoi. Survey. Bull. 422, 43. Proc. A m . So>. T e s t i n g M a t e r i a l s , 1 6 , 380 (1916).
Apparatus The method whereby the displaced volume is measured or weighed outside the parent volume and container was chosen as being in all probability the most practical. The apparatus hitherto used in this method is inadequate for the gravity determination of aggregat'es. In designing such an apparatus the following physical principles had t'o be considered: (1) A liquid such as kerosene is necessary as a medium of comparison and the surface tension of the liquid must be taken into account. The nature of the material determines the liquid to be used and the physical properties of the liquid the form of overflow tube required for an accurate displacement. (2) The material must be introduced beneath the surface of the liquid in order to diminish flotation of fine material. (3) Spreading of the material when entering the liquid is essential to air exclusion. (4). Control of the speed of introduction of the material into the liquid minimizes disturbances, splashing, and air inclusions.
Preliminary gravity determinations were made upon aggregates separated from bituminous pavements, using a liter side-tube flask with tube extended and bent down and a sleeve to introduce the aggregate beneath the surface of the liquid. Reasonably concordant results were obtained for displacements of 200 cc. or more. 7
Proc. A m . SOC.T e s l i n g M a t e r i a l s , 17, 2 5 i (1917').
INDUSTRIAL A N D E,VGINEERING CHEMISTRY
518
In an attempt to overcome the salient weak points of such an apparatus one was designed after the order of the Goldbeck apparatus.8 The essential parts are the special overflow tube and the combined lid. and funnel which are fitted to an ordinary battery jar. When simple straight or bent tubes are used, there is no sharp cut-off on the liquid flow, but a tendency to drip, especially when kerosene is used as the liquid medium of comparison, owing to its comparatively
Vol. 17, S o . 5
required, a metal with higher chemical resistance may be used. The stem is elliptical, with the least inside diameter 5 cm., making possible gravity determinations of both coarse and fine materials. The large inclined stem provides for the spreading of the material and a low rate of speed of introduction into the liquid, reducing to a minimum included air and loss from splashing. The stem extends 4 cm. beneath the surface of the liquid, thereby wetting fine material which tends to float when introduced upon the surface of liquids. The lid is provided with a flange which encircles the top of the jar outside, and the stem has sufficient clearance of the walls to permit the free turning of the combination about the top of the jar. The size of the container depends upon the capacity desired. A round battery jar 15 cm. deep and 12.5 cm. in diameter is a convenient size. A 1.5-cm. round hole is cut about 4 cm. from the top of the jar, in which the special siphon tube is inserted, stabilized by a cork collar or button of litharge-glycerol over the cork extension outside of the jar. The jar is of approximately 1.5 liters capacity to the overflow point and, being of glass, affords the operator an opportunity to observe the behavior of the material in the liquid. Operation
low surface tension. -4s such a drip might cause an error in the gravity determination, the principles of the siphon and capillarity were applied to overcome this difficulty. The siphon and internal diameter of the tube were varied and that giving the best results was adopted. I n designing a siphon that will give an abrupt break in the overflow of the liquid it is important that it shall be sensitive to the make as well as the break of the overflow column of liquid. It is desirable to be able to start the overflow of the liquid by a small volume displacement in order that the apparatus may not be limited in its use. A plain siphon with the initial end a t right angles to the plane of liquid level is sharp in cut-off, but leaves the liquid out of contact and far below the end of the tube. A comparatively large displacement is required to cause contact of the liquid with the end of the tube before the siphon will function. The inner end of the tube is therefore bent a t an angle of 90 degrees to form a miniature siphon. It is then cut a t such distance from the bend that a point inside the tube a t the apex of the throat of the miniature siphon and the highest point in the periphery of the bore of the cut end lie in the same horizontal plane. The incline of the free arm of the miniature siphon allows air to enter the upper part of the bore when the liquid is pulled away from the upper arc by gravity, and thus breaks the column of liquid maintained by the siphon effect of the tube as a whole. The tube outside the jar is gradually bent down, terminating vertically ahout 8 cm. from the plane of the liquid level, which permits emptying the tube by gravity when the column of liquid is interrupted by air, The interruption is intermittent to the point of equilibrium where the surface tension is not sufficient to start the miniature siphon. This leaves the tube primed for action, and a very slight rise of the liquid level of the jar-20 cc. or less-will cause the siphon to function and start an overflow of the liquid. The adaptability of the apparatus and the uniformity of introduction of the material into the liquid are regulated by a specially designed lid and funnel combined. The combin&ion is made%f heavy sheet copper with the stem of the funnel set into the lid a t an angle of 45 degrees. If U. S. Dept. A g r . , Bull.
949, 9.
The apparatus should be placed upon a stable base a t a suitable height for the receiving graduate, without change of position between the time of liquid level adjustment and that of volume displacement. It is important that the same procedure shall be used for the delivery of the liquid into the graduate, both in the level adjustment and the volume displacement. The material, previously dried a t 110' C., is introduced slowly into the funnel with the minimum disturbance of the apparatus and liquid and in quantity sufficient to allow for freeing the stem, before the overflow is interrupted, of any material that may have accumulated a t liquid level. A thin spatula is convenient for dislodging material from the stem a t the liquid surface, or it may be washed c down by a measured quantity of the liquid used as B medium, E c o r r e c t i n g for the 1 volume used in washing. \ Most materials are heavier than kerosene and readily settle o u t , so t h a t t h e special oVerflow .tube Figure 2-Funnel a n d Lid Combined works smoothly, thereby insuring the minimum disturbance within the liquid and apparatus: For aggregates containing fine materials which do not settle but diffuse upward through the liquid, a telescoped extension may be used on the funnel stem connected a t an angle of 60 degrees to vertical to retard the speed a t which coarse materials enter the liquid. In such a case a deep jar is necessary. In the apparent, specific gravity determination of porous materials, absorption may be corrected for by previously saturating the material, as in the Goldbeck method, or by determining difference in weight before and after saturation.
'\W,
The internal dieureter of the overflow tuhe and ~niuiatiire measuring, and gives ,nore coucordaut results witii a Iiiglier siplion requires modification according to the surface t.ensioii drgree of accurar,y. of the liquid to be uaed :is the medium of cumpariron. Table I ~ ~ - B l a n'Testa k ef 15' C
Results
Tahle I coirtains t,lir: r e d t s of I h r k t,e*t. Tor the a r : c i ~ ~ y arid i.ensitivcncss of the apparatus. The measured o r nriglrnl x
I!
19.6
19.8 19.6 19.9 19.8 19 8 19.3 I!! 8
I 0
-0
--l,
'I'dk I1
! il
-0 4 .-I) 6 -0 a -0 /i -11 2 -0.1
l!l.X
l8.li6 18..G 16.61, 18.82 16.56 16.li6 16.86 16.66 16.56
I(i.5U 16.50 18.lii 16 if, 16.Bi
I / $ ($4
givcs rcsulti of cuiqiurntive tests with this ai)-
%lid tlio
LeChatclier flnali, :mid with varying nlliwmts j,&.I
8indcr Ilituminuol aratedfrom the bitumen with carbon disulfide by m a n s of a Reeves inoditication OS the lfulin centrifuge, the reuiaiiiiug solvelit expelled by cautious heating, arid its gravity deteruiiued as separated Srmr the nrix. This tiible does iiot inoludc wrrections for loss or lack OS '
