INDUSTRIAL A N D ENGINEERING CHEMISTRY
222
Vol.fl9,'No. 2
Examination of Bone Black' By H. I. Knowles ATLANTICSUGAR REFINERIES, LTD.,SAINTJOHN, K.B
This paper is confined t o a consideration of color adsorption, ash removal, and hardness. The relation between t h e quality of bone black and t h e kind of bones used in its manufacture is illustrated by a comparison of bone black derived from shank a n d knuckle bones. This comparison includes a partial chemical analysis and color a n d ash removal tests. Decolorization is considered with respect to t h e quantity, quality, and distribution of t h e carbon of bone black. T h a t the carbon content is not always a criterion of char value, and t h a t there is a difference in carbon quality is shown by the comparison of shank and knuckle char and by a comparison of t h e carbon content a n d color adsorbed by this carbon i n t h e case of three different service chars. The optimum carbon content of bone black is suggested by t h e results of color a n d ash removal tests made on a char successively decarbonized and on another char, recarbonized. The same is also indicated by color and ash
removal tests made on chars which, during service, accumulated carbon. The selective action of bone black in removing salts from sugar solution is shown by t h e results of ash removal tests on granulated sugar solution, to which various salts had been added. These data suggest t h a t ash removal by bone black is a n adsorption phenomenon. The relation between color and ash removal, Brix, and the quantity of char is shown diagrammatically. This, together with t h e influence of the pH of t h e solution, is used to illustrate t h e necessity of conducting color and ash removal tests under carefully standardized conditions. A hardness test is described in which bone black is subjected to the impact and abrasion of steel balls in a small cast-iron ball mill. The increase in fines passing both a 24- and a 50-mesh screen is t h e measure used to express the hardness of the char.
E ARE told that granular bone black was first intro-
of char. Heat the mixture during 3 hours at 77" C. (170" F.) shaking the flasks gently for 30 seconds every half hour. Filter the solution through paper. Also heat and filter a blank sugar solution. Refilter all filtrates until sufficiently clear for color analysis. Estimate color spectrophotometrically and determine the ash content of the same solution by the sulfated method.
W
duced to the sugar refiner in 1828. Since then it has withstood all competitors, and today is the most important accessory used in the refining of sugar. For this reason, bone black offered to the refiner is worthy of critical examination and that in service should be examined a t frequent intervals. Such an examination may include a complete chemical analysis, a grist analysis, and a determination of the apparent specific gravity, color and ash removal, and so-called hardness. Only the three essential requirements of bone blackcolor adsorption, ash removal, and hardness, or resistance to mechanica! disintegration during service-will be considered here.
Table I-Grist
Analysis of S h a n k a n d Knuckle Bone Black
MESH
SHANK
KNUCKLE
Per cenl
Per cent
Raw Material The quality of bone black is related to the kind of bones used in its manufacture. Some authorities believe that beef bones make the best char. Not all the bones of an animal are of equal value, however. It is possible that some bones of other animals produce better bone black than certain beef bones. For instance, bone black made from hard tissue, like shanks or marrows, is generally superior to that derived from bones of a more delicate structure, such as knuckles. S H l K K AND KNUCKLE BONE BLAcK-Bones2 burned in a regular bone kiln were passed through a laboratory jaw crusher. The crushed bones were sieved and the fraction passing 14-mesh and remaining on 35-mesh was taken for examination. Screen analysis of the bone black gave the results shown in Table I. Color and ash removal was tested by the following method: Wash the char on a filter with 35 times its weight of water at 77" C. (170" F.) and then dry. Mix a quantity of char (the same quantity in each test) in a glass flask with a 50" Brix solution of a molasses sugar equal to twice the weight 1 Presented before the Division of Sugar Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. 9 Supplied through the courtesy of J. A. B. Ball, of the S t . Lawrence Sugar Refining Company.
This procedure was used in other color and ash removal tests herein reported. Table I1 gives the results of the chemical analysis. Table 11-Comoosition ~~
~~
~
of Shank a n d Knuckle Char
~
~
DETERMINATION
SHANKCHAR KNUCKLE CHAR
Per cent
Per cent 7.26 0.12 9.49 0.662
Carbon Insoluble in HCI Calcium carbonate Apparent specific gravity
16.37 0.96 7.48 0.502
Table 111 shows the color and ash absorption powers of the bone black. Table 111-Color soLU-
04,P:R;,
"IoN IN
1 2 3
I 1 1
a n d A s h Removed by S h a n k a n d Knuckle Char
COLOR REMOVED BLANK Shank Knuckle
1890 1000 528
Per cent 93.3 96.9 97.3
Per cent 97.2 98.4 98.1
1
ASH REMOVED
ASH IN
BLANK
Per cent 1.25 0.723 0.381
I
Shank
Knuckle
Per cent
Per cent
84.1
54.4 60.0 62.5
68.5
Owing to the greater decolorizing power of the knuckle char, it might be inferred that it is the better black. Bone black in service, however, is seldom called upon to filter
I S D U S T R I A L A X D ENGINEERIAVGCHEAV1J'TRY
February, 1927
sugar solutions of color much over 1000 units and the greater proportion of sugar liquor has a color of less than 500 unite. I n practice, therefore, the shank char would probably be found as good a decolorant as the knuckle black and in addition it would remove more inorganic matter. Decolorization
It is generally recognized that decolorization is an adsorption phenomenon. This, in conjunction with what is known about the active and inactive forms of carbon, explains much of the decolorization differences of various chars. It also shows that the carbon in bone black must be considered with respect to quality, quantity, and distribution. Reference to the carbon content and color adsorption of shank and knuckle chars shows that the carbon content is not always a criterion of char value, and that there is a difference in carbon quality. Presumably, the treatment bones receive prior t o conversion t o bone black influences carbon quality. The activity of the carbon of service chars apparently is not always the same. This was shown by a comparison of the carbon obtained from three service chars ( A , B , and C). A is the oldest and poorest; C is the newest. In addition t o washed sugar liquor, -4 is called upon to filter such liquors as char water and affination sirup. With the exception of washed sugar liquor, B and C filter only char-filtered liquors. Table IV shows the carbon content of the three chars and the color adsorbed by the derived carbon. Table IV-Decolorization BONE
d is attributable to the increase in porosity of the char. In B the small differences are probably due to incomplete removal of bone oil during heating. During the same period bone black which in service accumulated carbon showed the changes given in Table VI. B was being gradually replaced by char of about 10 per cent carbon content and A was replaced by B char-i. e., by char of about the same carbon content. The peak of decarboiiization was reached after 15 months, when the carbon content had become about 7 per cent. The decolorizing power then began to decline. After 5 months it was back again t o a value corresponding to a carbon content of about 3.75 per cent. Other factors influence the activity of service char, but during the period under consideratioii conditions were much the same. It is likely, therefore, that the activity noted is in large measure the result of carbon chanqes in the
b y Carbon of Bone Black
BLACK
'4
B
C
P e r cent
Per cent
15.73 6.81 7.69
73.8 85.8 86 1. 72.5 72.6
.
.I (decarbonized)
As adsorption is a surface phenomenon, it is conceivable that there is an optimum carbon content of bone black depending upon the available bone surface area. This would correspond to a carbon layer of some definite thickness. A deeper layer would tend to cover underlying carbon and reduce the pore area, thus decreasing adsorption. Less carbon would reduce the carbon surface area with the same result. If this be true, what is the optimum carbon content of bone black? We may seek an answer by examining the results of some decarbonization and recarbonization experiments conducted with service chars. Table V shows the results of color and ash adsorption tests made on A char decarbonized and B char successively recarbonized with bone oil. Table V-Color
223
a n d As11 Removed b y Decarbonized a n d Recarbonized Bone Black
CARBON
COLOR
REMOVED
ASH
REMOVED
Per cent Per rent A (decarbonized char) 15.73 53.2 14.5 13.97 53.8 28.7 9.26 64.7 36.3 3,915 42.1 74.5 70.5 34 B (char recarbonized with bone oil) 3.47 66.7 29.6 5.62 75.6 35.6 a.71 32.1 77.0
Peu ce17l
I).
The results in Table V are suggestive rather than conclusive. In both chars the optimum carbon content appears to be about 6 per cent. The increase in ash removal of
/
was responsible. With regard t o new bone black, the optimum carbon content obviously is the maximum consistent with maximum ash removal and hardness. Taking shank char as a standard, the optimum would appear t o be between 9 and 10 per cent carbon. New bone black with a carbon content much lower than 9 per cent would probably be deficient in decolorizing power. A new char having more than 10 per cent carbon would probably remove less ash and be more susceptible to shrinkage during service. Ash Removal
Removal of inorganic matter from sugar solutions by bone black is generally attributed to the inorganic constituents of the char, principally the bone itself. Investigators have found that the action is selective. S o t having the results of these investigations available, the writer conducted some experiments to show this selective action. T o several portions of a 60' Brix granulated sugar solution were added various salts in quantities approximating 0.5 per cent of the sugar solids. The solutions were digested
14VDL'STRIAL A S D E.VGI.VEERISG CHEMISTRY
224
for 3 hours at 82" C. (180" F.) with a quantity of bone black equivalent to 100 per cent of the sugar solids present. Filtration through paper followed. Ash was determined by the sulfated method. I n the results giren, however, the customary correction of -0.1 has not been applied. I n some cases a n analysis was made to show selective removal of ions. The results in Table VI1 support the generally accepted views regarding the removal of salts by char. The action of char in this respect is complicated by the exchanging of some of the base. Thus, a qualitative analysis of solutions showing an increase in ash demonstrated that lime, presumably derived from the calcium carbonate of the char, I
CARBOX
1
After 20 months ~~
Per cent
Pw cent
3.76 3.85
7.02 7.59
~~
Per cent 8.00
7.90
1 I
i
KCI KzS04 NaCzHaOz KzCzOr CaCh CaSOda Mg(Ii03)z FeSOn FeCh NaHzP04 CaHa (Pol)z Blank
1
0.326 0.276 0.155 0.283 0.301
0.286
' 0.103
2.5i.l 26.3 29., j 41.4 7.7 68.2
13.6b 72.0
0.103 0.170 31.8b 0.234 60.2 0 . 2 8 6 _ _ 95.0 0 . 0 0 5 , t I24.2b
i
6.6 6.6 6.0 6.8 6.7
Initial
After 15 months
Per cent 73.2
Pev cent 82.0 90.3
Per cent
Per cent
Per cent
87.4
~
7.3 8.3 7.6 8.5
6.9
I
SO4 C1
...
! ${ ~
6.9
6.8
6.6 5.0
6.9 6.5 5.9
%
R
0.134 0.148
45.5
...
SO4
0:Ok84 ni:; 0.0738 0.0277
...
...
-*
Ca
... ...
...
REMOVED
Initial
SALT
%
ASH
After 20 months
of S a l t s a n d I o n s by B o n e B l a c k
~~
The so-called hardness of bone black is not easily defined or measured. Presumably the real hardness of various kinds of bone is much the same. As applied to bone black the term hardness possibly refers to the structural strength of the particles of bone. Thus a very porous bone of honeycomb structure would not be expected to resist impact as well as a more solid bone. The shape of the bone particle would also be a factor. Spindle-shaped particles would tend to break UP more readily than round particles. Any test for hardness, therefore, should recognize, and distinguish between, the various factors which determine t o
After 15 months
had gone into solution. This was particularly true of the ferric chloride solution, from which iron was almost completely removed. I n the magnesium nitrate solution, less magnesia was present after char filtration. The increase noted for the potassium chloride solution can be accounted for to a large extent by the increase in ash of the blank solution. Of particular interest is the removal by char of calcium acid phosphate and the phosphate ion. Similar treatment of sugar solutions containing iron tannate and iron pyrogallate in quantities equivalent t o 0.012 and 0.011 per cent Fe203, respectively, removed the pyrogallate completely, but not the tannate. Removal of the tannate mas nearly complete, however. T a b l e VII-Removal
Hardness
COLOR.\BSORRED
After 15 months
A B
Vol. 19, s o . 2
2.lb
...
... I.-
12.0 f i i
63.7 46.2
...
... ...
a Calcium saccharate a n d sulfuric acid were added t o a granulated sugar solution a n d the precipitated calcium sulfate was filtered off. E r i dently the solution contained calcium oxide in excess of the SO4 equivalent. b Per cent increase. c Less than 3.1.
The extent to which the different ions are removed is suggestive of adsorption. This, in conjunction with the fact that ash removal by bone black depends upon ash concentration, indicates that ash removal is an adsorption phenomenon. If then color and ash removal by bone black are the result of adsorption, it follows that any test devised to measure color and ash adsorption must take into account color and ash concentration. I n addition, Brix is an influence of no small import'ance. The relation between color and ash removal, Brix and the quantity of char is shown in the accompanying diagram. The apparent amount of coloring matter in a sugar solution is influenced also by the pH of the solution. The influence of the several factors considered demonstrates the necessity of conducting color and ash removal tests under carefully standardized conditions.
-
74.0 87.8
After 20 months
Per cent 35 50
what extent a bone black might be expected to resist impact and attrition during service. A number of years ago, Horne devised a test for hardness by rotating bone black in a tin can with marbles and measuring the increase in fines. The writer has elaborated this test by using a cast-iron ball mill, of the turnip type and 11/4 pounds dry capacity, and 10 steel ball-bearing balls, 6/g inch in diameter. When rotated a t about 30 r. p. m., the char and balls run together down the side of the mill in a position a t about 45 degrees to the horizontal. I n developing this hardness test, it was early recognized that to get an adequate expression of hardness, char subjected t o test must be gristed within rather narrow limits. The grist 16 X 24 was chosen, in the belief that it would include the larger portion of either a 16 X 30 or a 10 x 28 bone black. For purposes of test, the sample of bone black is therefore siered to obtain the 16 X 24 fraction. One hundred grams of this fraction are sieved on 24-mesh and 50-mesh sieves for 10 minutes, using a Ro-tap mechanical sieve shaker. The portions passing the 24-mesh and 50-mesh sieves are weighed. The three fractions are reunited and put in the ball mill with the steel balls. After rotating the mill for 15 minutes, or for 450 revolutions, should the speed be somewhat different than 30 r . p . m . , the char is removed and resieved. The total net loss on 24-mesh has been termed the "shrinkage number," and the net gain through 50-mesh has been designated as the "discard number," it being assumed that in practice char finer than 50mesh would be removed by screening. Duplicate tests give results that seldom vary more than 0.5 for the shrinkage number and 0.2 for the discard number. Some results of this hardness test are given in Table TIII. T a b l e VIII-Results
Shank Knuckle New New Service A Service B Service C
11.9
17. 12.2 16.5 5.2 9.4 10.9
of H a r d n e s s T e s t o n C h a r
2.4 2.4 2.1 3.1 0.5
Used 30% 14 X 16 mesh Used 70% 16 X 24 mesh Good char Poor char Oldest
1.5 1.9
Newest
...
Experience with this test is limited. From the results so far obtained, however, i t expresses satisfactorily differences in the quality of bone black and hardness as judged by color and ash adsorption tests, specific gravity, and resistance to crushing between the fingers. Thus, a good char will show a shrinkage number of 12 to 13 and a discard
February, 1927
ISDCSTRIdL, A S D ESGIA-EERISG CHE-IfIISTRY
number of 2 to 2.5. Poorer blacks give corresponding numbers of 14 to 17 and 3 to 3.5. The values for service chars show that new char is soon reduced to a shrinkage number of about 10 and a discard number of about 2 and that during service the softer, friable particles are discarded. There is suggested also the possibility of using the test to determine undue shrinkage as the result of faulty handling of the black during service. Conclusions The examination of new bone black begins with the identification of the types of bone that have been used in
225
its manufacture. Much information on this point can be obtained by a visual examination of the char particles, by the apparent specific gravity of a definite grist of the black, by the carbon and calcium carbonate content, and by color and ash adsorption tests. As color and ash adsorption are influenced by such factors as Brix, pH, concentration, and quality of color and ash, it is necessary to conduct color arid ash adsorption tests under carefully standardized conditions. A standard char should be included for reference and comparison. It is believed that the important property of socalled hardness is satisfactorily measured, for comparative purposes, by the test here described.
Electrolytic Conductivity of Solutions of Granulated Beet Sugars' By A. R. Nees THEGREATWESTERNSUGARCo., DENVER, COLO.
METHOD for determining the ash content and purity of granulated sugar by means of the electrolytic conductivity of the solution has been under development in this laboratory for nearly two years, and for the past year it has been employed as a routine test with yery satisfactory results. Ot,her workers2 have recently reported the use of this method for the determination of ash in ram sugars and certain refinery products. Apparently most of these investigators have used the apparatus and method of Toedt, which seem to give very satisfactory results. Not knowing of the existence of such an apparatus, the writer devised one to meet his own requirements, using standard equipment throughout so that it can be easily duplicated a t a reasonable cost.
A
Apparatus The apparatus is of the type which utilizes the current from a 110-volt', 60-cycle lighting circuit. It consists of a one-toone transformer, the purpose of which is to prevent injury to instruments through grounding of the circuit; an alternating current galvanometer; a dial-type Wheatstone bridge, and a conductivity celL3 The use of the galvanometer instead of the telephone receiver is a decided advantage. The dialtype Wheatstone bridge is much more conrenient than the usual slide n-ire and resist'ance box hook-up. While the apparatus of this type is not of the highest precision, it is rugged and dependable and will give a higher degree of accuracy than is ordinarily demanded in process control work. The manipulat'ion is simple and rapid; one man and a helper frequently make one hundrcd and fifty determinations in 8 hours. Determinations The determinations are carried out a t 25" C. using a solution containing 25 grams of sugar per 100 ml. The temperaPresented under the title "Electrolytic Conductivity of Solutions of Refined Sugar" as a part of the Symposium on ' Refining of Sugars" before the Division of Sugar Chemistry a t the 72nd ,Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. Zerban a n d Mull, Facts A b o u t Sugar, 21, 278 (1926); Toedt, Z . V e r . deut. Zuckeuind., 7 5 , 429 (1925); I n t e r n . Sugnv J . , 27, 503 (1925); Lunden, Z. V e r . d e u t . Z u c k e r i n d . , 7 5 , 763 (q.5); Inlern. Sugar J . , 27, 671 (1929). The alternating current aalvanometer is Leeds & NorthruD No. 2370-b; the Wheatstone bridge is L. & N.No. 4 i 6 0 ; the conductivity cell is L. & N. No. 4911.
ture control is quite important. For routine work where a large number of samples are to be tested, a thermostatically controlled water bath is necessary. If only occasional samples are being run, it is quite satisfactory to take about three readings between 24" and 26" C. and determine the reading a t 25 C. by graphic interpolation. It has been found convenient to express all results in terms and to transof specific conductance (as niultiples of late this figure into terms of ash and purity as occasion demands. The calculation is made according to the equation: O
C L = 11
where
L
= specific conductance
C
= =
R
conductivity cell constant resistance
A correction is made in the usual way for the conductance of the water. It is advisable to use freshly distilled water having a specific conductance of about 0.25 X reciprocal ohms, but especially prepared conductivity water is not necessary. The constant of the conductivity cell is determined by using a 0.001 S potassium chloride solution, the specific conducta t 25" C. The proper ance of which is taken as 14.72 X water correction is also made in this case. The relation between specific conductance and ash was determined by comparing the conductance figures Tvith the ash as determined in the usual way for a large number of samples of varying ash content. This relation was found t o be a straight-line function over the range ordinarily encountered in refined sugars. Later determinations of ash showed the established relation t o be reliable within the limits of accuracy of the direct method. The slope of the line was found to be such that tan e = 231.5 when specific conductance X 10-5 is plotted as ordinate and per cent ash as abscissa. Therefore the per cent ash may be determined by dividing the specific conductance X by 231.5. This value was determined for average beet sugars produced in Colorado, Sebraska, and Montana, and would undoubtedly be applicable to any beet sugar containing ash of similar composition. The ash-conductance relation for refined cane sugars has not been investigated. It is probably slightly different from that found for beet sugars because of relatively large percentage of highly ionizable alkali salts present in the ash of these sugars. The purity calculation is based on the fact that in beethouse products there exists a fairly constant and definite
