I-VDUSTRIAL ALVDENGILVEERIiYGCHEMISTRY
December, 1929
of increasing hygroscopicity used which yielded a set of results worthy of record. The success attained by Lowry and Kohman (13) in altering the water absorption of a thoroughly washed rubber by milling sodium chloride into it is worthy of mention in this connection. The presence of the calcium chloride in the experimental stock of the present test so increased the time of cure that the slab cured for 60 minutes a t 160" C., and used in the test, was apparently undercured. This slab was placed in a desiccator over calcium chloride immediately after being cured. The results of permeability tests carried out in the usual manner are shown in Table IV. of H u m i d i t y of Air on P e r m e a b i l i t y of a R u b b e r Stock C o n t a i n i n g Calcium Chloride PERMEABILITY TREATMENT PRIORTO TEST Liters per hour per sg. m. exposed 0.19 Stored over CaCh 0.18 Exposed to atmosphere 2 hours, (ret. hum. 26%) Exposed to atmosphere 20 hours 0.19 Exposed to satd. atmosphere 4 days 0.16 Exposed to satd. atmosphere 8 days 0.17 T a b l e IV-Effect
from these various i:omparisons In drawing it seems to be justifiable to state that moisture is capable of
1219
affecting the permeability of rubber to air. The effect of the moisture in the atmosphere is small, however. Acknowledgment
The authors wish to acknowledge their indebtedness to X. A. Shepard for counsel and to the Experimental Engineering Laboratory of t,his company for assistance in the construction and maintenance of the apparatus. Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
Anon, India Rubber J.,76, 217 (1928). Cagniard-Latour, J. Franklin Inst., 24, 117 (1839). Daynes, PYOC. Roy. SOC.(London), 97A,286 (1920). Daynes, Trans. Inst. Rubber Ind., 8, 428 (1928). Dewar, Proc. Roy. Inst. Gt. Brit., 21, 813 (1915). Dubosc, Rev. gbn. caoutchouc, 39, 7 (1928). Edwards, India Rubber J., 66, 821 (1918). Edwards and Pickering, Bur Standards, Tech. BuU. 387 (1920). Graham, Trans. Roy. SOC.London, 156, 399 (1866). Grenquist, IND.ENO. CHEM.,21, 665 (1929). Hauser, Kaulschuk, 5, 151 (1929). Kayser, Ann. Physik, 43, 544 (1891). Lowry and Kohman, J . Phys. Chem., 31, 23 (1927). Mitchell, A m . J . d4ed. Sci., 7, 36 (1830). Schumacher and Ferguson, IND. ENG.CHEM.,21, 158 (1929). Wrohlewski, pogg. Ann., 168, 539 (1876).
Factors Affecting the Drillability of Fertilizers' Arnon L. Mehring BUREAC
OF
CHEMISTRY
A N D SOrLS,
U.
s.DEPARTMENT OF
AGRICULTURE, WASHINGTON, D. C
Tests in several standard distributors of materials H E use of c o m p l e t e and of injuring the plant. It and mixtures representative of the fertilizers now in mixed fertilizers began is difficult to adjust presentuse and proposed for use showed that their drillability about 1860 and was day distributors so that they varied greatly with changes in relative humidity and widespread by 1880. Alawill make applications at a only slightly with differences in temperature. All the chines f o r spreading lime, desired rate. This difficulty fertilizers could be drilled satisfactorily at any humidplaster, ashes, and guano had increases with low rates and ity below 50 per cent, but none when exposed for a few been invented before the init is also harder to distribute days to a humidity above its hygroscopic point. Masmall applications uniformly. troduction of complete mixterials containing a considerable proportion of particles The present tendency, howtures, however, and these mafine enough to pass a 200-mesh screen were unduly chines, with or without modiever, is toward smaller apdusty when dry and undrillable when slightly damp, plications of fertilizers that fications, were employed for while those consisting of particles between 5 and 80 the distribution of the new cost more per pound. Hence mesh were easily drilled when slightly damp and could fertilizers. Some of t h e s e elimination of wasteful or inbe distributed in every case in atmospheres below their distributors were identical in efficient methods of applicahygroscopic points. The drillability of a fertilizer principle with implements in tion is becoming more imvaries inversely with its kinetic angle of repose. Mixed use today. portant. fertilizers composed of particles of different size, shape, Extravagant claims were The difficulty of obtaining and specific gravity were found to segregate more or made that these early maexact delivery rates and uniless during distribution causing in some cases marked chines would d u s t e v e r y form distribution with preschanges in the ratio of plant food elements delivered square inch of the soil evenly ent implements is due partly from time to time. The nearest approach to perfect with an application as small to the design and construcdistribution was obtained with a fertilizer composed of as one-half bushel of plaster tion of these implements and 20- t o 30-mesh rounded particles and having an angle or bone d u s t to the acre partly to the variability of of repose of 40 degrees. and that the quantity sown fertilizer p r o p e r t i e s . The could be remlated to within purpose of the work reported one pint per acre. Such precision would have been highly here was to gain a better understanding of the factors that desirable with the ordinary mixed fertilizers of years ago affect the drillability of fertilizers. Such knowledge should but the need for uniform distribution and accurate con- facilitate both the manufacture of fertilizers of better drilltrol of the quantity applied is now greater than ever, as ability and the designing of more efficient distributors. highly soluble chemicals are being substituted more and more Experimental Method for insoluble organic substances, while the concentration of fertilizers is increasing. Greater care must be esercised in Since the mechanical condition of a fertilizer changes applying these chemicals to crops because of the greater danger of delaying or preventing germination of the seed rapidly with variations in atmospheric conditions, satisfactory observations on the drillability of fertilizers cannot be 1 Presented before the Division of Fertilizer Chemistry a t the 78th mnde in the field. A laboratory was therefore constructed Meeting of the American Chemical Society, Minneapolis, Minn , September 9 to 13, 1929. in which the relative humidity and temperature of the air
T
w i s t i i i i t i l , i loi~,gp r i u d s OS t i m e or varied at will ritliiii the range ordiiitirily encountered OUtdooTS. In the experiments t.o he described the relative liumidity \vas varied Srom 20 to 90 per cent, wliile the t.emperature was held const,ant at 68" F., then tlie temperiiture was varicd from 5O0 to 86" F.,while the relative liumidity was lield constant. at 60 per cent. Sirieteen fertilizes materials and 24 mixtures, wliioli are believed to be fairly repreptative of tlie goods now in use or proposed for use, were selected. The materials were of tlie usual commercial grade and tlie mixtures included ordiiuiry: liigli-analysis and concemtrated couimereial goods, x s noli 8s :i fc\v very highly coiiceirtratted special mixtures.
r:~>iilil/)r li(dii
Fieure 1 -Interior of Consfnnf Humidity Room
About 50 pimids of each fertilizer were spread in shallow. burlap-bottomed trays, which were then placed on racks in the constant-humidity rnom so that a fan could circulate air around them (Figure 1). The atmospheric conditions in the room were held constaxit to within z/,o degree of temperature and 1 per cent of humidity for long periods of time for each of the combinations sliown in the tables. During tlie first 3 or 4 n-eeks the trays were weighed and the contents were well mixed daily until cessation of absorption OT evaporation of moisture was shown by constant weight for at least three days, when the moisture was determined in diiplicate hy drying samples t.o constant WCig1it in a vaCuum desiccator containing dry pliorphoriis pentoxide. The fertilizers were then ready for testing in distributor.. I.ater tlie existence of equilibrium was demonstrated liy returning to the same coiiditions from the opposite side of equilibriuni mid obtaining praet.ically the sanie experimental resu1t.s. Ten distributors, represeiitiirg t,ypes commonly used for applying fertilizers t o cotton; corn, potatoes, and small grain, were used in this study, but all the results given iri the present, paper were ohtained with a star feed grain drill attaeliment. This implemeiit was used because it is representative of one of the priiicipal iypes now in use in this country. It has a wide range of delivery rates and is capable of conreiiient mid positive adjustment. This implenient was installed in the constant humidiiy room and was run by an electric mot,or at a speed usually empiuyed in tlie field. A revoiution count,cr was mounted on the ground wheel axle. It was Sound that t.he feed wheels eould be started and stopped simultaneously with tlie recording of a revolution by means of tire clutch on tlie machine. Weights of fertilizer delivered when the machine was run a t t.he number of revolutions corresponding to an
ndvancc in the field of 100, 1000, a i d 1000 foeb were id/ exact multiples of tlie lowest weight t o within 0.01 pound. It is believed, therefore, that no error was introduced in starting and stopping the. drill. The gate lever was set at notch 10, whicli, according t i , the manufacturer's table, should give :irate of 80 pounds per acre witlr tlie low-speed gear. This is a h i t tire rate that probably would be most used with conceiitrated Sertilizers. In practically all of the experiments both highspeed and loiv-speed gears were uscd. As the high-speed gears gave rates almost. exactly 4.5 times tlie rat.cs of the low-speed gears, other conditions being tlie same, only the low-speed rates are given here. In making a test, the liopper was filled to a depth of 8 inches and the machine was run iiiit,il fertilizer was flomiiig normally from all units, when the clutch was tlirown init and the materid delivered was retiirned to the hopper. The itmehino was then started again. Wlieri the revohitioii counter registered a number comspondinp to 1000 feet oS zdvance, tlie machine was stopped and the fcrtilizer deposited in a pan beneath the delivery tubos was weighed accurately. -4t least tlirce deterrninatioiis were made in 11 case. It mas found that t,he principal prnpert,irs of fertilizcri iijl'ecting their distributing qualities are hygroseopicity, state of subdivision, degree of physical Iieterogmeit,y, appareiit specific gravit.y, and the friction and cohesion betn-een particles. The mechanical condition of the fertilizer at any tiine also depends largely upon the i\-eather to rrlriali it litis been exposed. Effects of Weather Relative liuiiiidity and temperature are the (hief elements uf the weather that are ca,usalIyrelated to variations in ferlilizer properties. Hurnidit,y, being of greatcr importance, is considered first. Table I shows the delivery rat.es on the inoist basis arid tlre water content of the fcrtiliaers, obtained under equilibrium conditions at 68" F. and various relative humidities. Xitrate of lime was perfectly dry and drilled exceptionally well in ail atmosphere of 40 per cent relative humidity. At -50 per cent relative humidity it was soggy with moisture and drilled very poorl?.. At 60 per cent it had entirely liquefied. Sodium nitrat,e drilled excellently a t 40, 50, and 60 per rent. rclat,ive humidity, but could not he halidled in this distributor when tlie relative humidity was 70 per cent or higher. Of t,he new concentrated riitrogenous f e r t i h r s urea, ammonium nitrate, and Leunasalpeter behaved much like nitrate of soda, although U X ~ ,like animonium sulfate, could he drilled at humidities 10 per cent higher than could nitrate of fioda. Superphosphate was too dusty at 40 per cent relative hrimidity and too damp at 90 per cent for good results, hut it, could be distribut,ed at any Iiurnidity below 90 per cent. I t did best at 70 or 80 per cent. The concentrated phosphates, animrr-plios, monoammonium phosphate, triple superpliosphate, potassium ammonium phosphate, and monopotassiimi pliospbate, drilled excellently :it all humidities up to atid including 90 per cent. Iliammonium pliospliate was fully as satisfactory as sulfate of ammonia but not nearly so good as monoammoniuni phosphate. It gave off ammonia and heeame a pasty mass at. 90 per cent relative humidity. Peat was unpleasantly dusty in a dry atmosphere and fish scrap and cottonseed meal decayed in an atmosphere of 90 per cent relative humidity. These materials as a class differed from the water-soluble ones. They distributed a t practically the same rate per acre at every degree of humidity,
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1929
while the delivery rates of the chemical fertilizers, with the exception of potassium ammonium phosphate, diminished as the humidity increased. The variations in delivery rate were of the same order for the mixtures as for the individual materials. As a class the commercial double-strength mixtures were less affected by high relative humidity than were similar mixtures of ordinary or of very concentrated grade. This was probably due to the nature of the particular mixtures involved and does not imply a fundamental difference. The effects of temperature changes over the range ordinarily encountered are less than those produced by relative humidity, as is shown in Table 11. Almost without exception the water content was lowest and the drillability best when the temperature was lowest. The nitrates were more and the phosphates less affected by changes in temperature when other factors were held constant than were other classes of fertilizers. The variability of the effects of relative humidity and temperature on the drilling properties of fertilizers are clearly due to the hygroscopicity of the materials themselves. This is evident when the delivery rates already given are studied in the light of the data on the hygroscopicity of fertilizers presented by Ross, Mehring, and Merz (3) and by Adams and Merz ( I ) . Effects of Physical Properties of Fertilizers
Some of the differences in delivery rates shown in Table
I for substances of equal dampness are due to the apparent T a b l e I-Effect
1221
specific gravities. When rates are computed in pints instead of in pounds less discrepancy exists (Table 111). A certain variation, however, still remains and part of this is due to differences in the size and shape of the particles of which the fertilizers are composed. Particle size was studied, among other ways, by carefully screening ammonium phosphate into size fractions and comparing them by distribution under controlled conditions in the same way as in the experiments already described. The sizes included 5-10, 10-20, 20-40, 40-80, and 80200 mesh and particles finer than 200 mesh. . After each test the materials were rescreened to remove broken particles. The delivery rates and moisture contents at equilibrium are given in Table 111. The delivery rates by volume, where the effects of specific gravity are lacking, show that particle size makes no practical difference at humidities of 70 per cent or lower, except in the case of the finest material, which was almost as fine as wheat flour. The effects of increasing the humidity were very pronounced with this 200mesh material, but rapidly diminished with increase in particle size. High relative humidity had very little effect upon the 5-10 mesh sample. While a number of the fertilizer distributors on the market are claimed to be of the force-feed type, most of them depend to a considerable extent on gravity flow for delivery of the fertilizer. The delivery rate of any given material with a fixed setting of the machine depends more or less upon the flowing properties. The rate of flow of fertilizers was recently studied by Deming and Mehring ( 2 ) and a
of C h a n g e s in Relative H u m i d i t y a t 6 8 O F. u p o n t h e W a t e r C o n t e n t of Fertilizers a n d T h e i r Delivery R a t e b y a S t a r F e e d G r a i n Drill Fertilizer A t t a c h m e n t
(Calculations on Moist Basis) AT 40 PER CENT i T 50 PER CENT
FERTILIZER
Ordinary fertilizer materials: Superphosphate Sulfate of ammonia Nitrate of soda Nitrate of lime Fish scrap Cottonseed meal Peat Concentrated fertilizer materials: Urea, granulated Urea, ammonium phosphate Ammonium nitrate Leunasalpeter Ammo-phos Monoammonium phosphate Diammonium phosphate Triple superphosphate Potassium ammonium phosphate Monopotassium phosphate Potassium nitrate Trona potassium chloride Ordinary commercial mixtures: 2-8-5 3-9-3 4-8-4 9-0-6 High-analysis commercial mixtures: 4-10-8
io-S-io
12-6-2 Concentrated commercial mixtures: 0-20-20 4-16-10 4-24-4 8-12-20 8-16-8 10-16-14 Concentrated special mixtures: 14-42-14 14-43-14 13-39-13 13-39- 13 13-4 1-1 3 17-26-17 14 remaining drillable a t 90 per cent relative humidity (av.) Undrillable because of ahsorption
Water con. tent
Deliver1 rate
'er cenl
Pounds
'er cent Pounds
0.44 0.03 0.23 14.79 5.60 6.82 11.69
102.95 82.76 135.04 100.48 58.95 48.35 91.04
0.87 0.12 0.40 24.77 6.58 7.47 12.90
0.07 0.11 0.02 0.09 0.76 0.29 0.24 2.44 0.23 0.14 0.27 0.14
73.33 78.41 96.41 88.28 80.59 104.98 66.79 115.87 65.05 117.18 123.71 104.11
2.54 3.42 2.33 3.75
4 T 60 PER CENT
>er cent
Pounds Per cenl
Pounds
7.54 8.93 14.12
56.34 45.30 89.88
8.80 12.24 15.39
54.89 43.85 90.16
70.57 70.42 89.18 82.62 81.02 104.98 63.60 113.98 66.21 112.68 118.05 92.20
0.31 0.53 0.38 0.31 1.21 0.42 1.23 4.45 0.43 0.47 0.29 0.20
63.45 66.50 73.33 76.08 84.07 101.20 59.53 111.51 67.66 105.27 115.43 77.54
0.76 4;39
55.90 5.81
4.03 1.63 0.51 1.61 6.86 0.65 0.82 0.44 1.38
9.00 84.66 96.12 55.61 107.16 67.23 94.82 96.70 53.72
8.36 0.61 4.99 9.83 1.03 1.25 0.61 4.96
65.63 90.75 6.82 106 58 63.31 85.38 86.83 28.17
2.80 4.89 3.39 5.86
85.96 74.05 91.04 67.66
3.90 7.57 4.64 8.66
78.55 73.33 81.31 61.13
10.91 15.43 15.13 15.04
59.97 63.45 56.19 5.52
29.96 24.83 28;28
1.89 15.25 9,l5
94.09 94.67 88 28
2.00 2.97 6.98
83.34 97.14 60.84
2.76 3.57 8.12
82.18 94.38 55.32
7.25 4.94 14.72
67.52 84.65 10.45
15.09 19=16
0.85 2.14 1.42 1.79 2.02 1.72
118.34 92.64 81.75 98.30 105.56 93.94
1.35 2.80 3 31 62
2 96 2.06
107.30 90 46 79 42 96.56 101.93 92.93
1.64 3.96 5.27 3.37 3.81 2.77
96.85 86.83 75.79 93.94 90.60 89.59
6.09 9.98 11.65 5.46 6.23 8.24
86.54 69.12 69.41 89.44 80.44 56.34
0.05 0.32 0.58 0.37 0.60
99.75 53.58 104.98 109.05 104.54 95.69
0.12 1.35 0.83 0.51 0.14 1.12
96.56 46.46 98.74 107.88 101.35 88.43
0.31 3.83 1.20 0.79 0.26 1.79
82.33 33.84 91.62 96.99 90.31 78.99
4.69 8.50 4.19 4.24 1.04 6.22
2.57
100.10
2.06
97.19
2.74
92.58
4.49
87.85 78.26 93.36 84.07
1.30 2.44 1.80
0.08
moisture.
b
In solution.
c
Decomposed
I
3.10 2.90
79.57 11.76
b b
b
b
AT 90 P E R CENT
Der cent Pound: 'er cenl
1.96 0.53
0.14 0.35 0.17 0.19 0.95 0.31 0.74 3.24 0.30 0.24 0.28 0.16
85.67 51.55
AT 80 PER CENT
93.65 69.12 112.09
100.77 82.47 125.45 24.39 58.08 47.04 90.31
1.05 0.23 0.51
I AT 70 PER CENT
11.86 13.35 16.82
53.14 52.27 89.46
14.82 b b b
Founds 57.35
c c
19.46
87.99
b b b b
(1
16.27 4.17
34.27 71.00
16.92 6.02 3.27 lh35
90.60 71.44 39.64 80.44
a
rl E (i
58.23 22.94
33.65
21.69 22.76 11.87 11a86
35.43 60.84 53.72 60.26
41a19
8.42
19ao1
55.76
9.87 14.37 57.06 62.58 65.34 17.71
7.61 7.01 3=31
33.69 12.78 22.94
21.12 15.32 10.65
3.92 4.21 4.50
80.35
7.80
65.45
15.94
43.81
a
3.78
a
(1
a
0 (I
a
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
1222
T a b l e 11-Effect of Air T e m p e r a t u r e C h a n g e s , a t 60 P e r C e n t Relative H u m i d i t y u p o n W a t e r C o n t e n t of F e r t i l i z e r s a n d u p o n T h e i r R a t e of DeliGery b y a S t a r Feed G r a i n Drill Fertilizer A t t a c h m e n t
1
A T ~ ~ O F1 . AT 8 6 ' F .
AT 50° F. De-
' ;2
FERTILIZER
rate per acre
De-
1
De-
acre
I
acre
water 'On-
tent
I
per Poutids cent
Ordinary fertilizer materials: Superphosphate Sulfate of ammonia Nitrate of soda Nitrate of lime Fish scrap Cottonseed meal Peat concentrated fertilizer materials: Urea, granulated Urea, ammonium phosphate Ammonium nitrate Leunasaloeter Ammo-pkos Monoammonium phosphate Diammonium phosphate Triple superphosphate Potassium ammonium phosphate Monopotassium phosphate Potassium nitrate Trona potassium chloride Ordinary commercial mixtures: 2-8-5 3-9-3 4-8-4 9-0-6 High analysis commercial mixtures: 4-10-6 10-8- 10 12-6-2 Concentrated commercial mixtures: 0-20-20 4-16-10 4-24-4 8-12-20 8-16-8 10-18-14 Concentrated special mixtures: 14-42-14 14-43-14 13-39-13 13-39-13 13-41-13
99.17 21.58 126.90 3.05 59.39 48.79 92.78
0.95 93.65 1.05 0 . 2 2 69.12 0 . 2 3 0 . 3 2 L1Z6O9 0 . 5 1 24.95 7 . 3 6 56.34 7:k4 8.87 45.30 8.93 12.70 8 9 . 8 8 14.12
Per 87.41 1 . 2 0 60.11 0.31 84=5l 1.17 56.34 7:55 45.74 8 . 8 8 85.52 1 5 . 0 5
70.86 75.65 83.34 90 60 84.22 104.83 63.89 118.48
0 . 0 5 6 3 . 4 5 0 . 3 1 58 0 . 1 1 66.50 0 . 5 3 34 0.08 7 3 . 3 3 0 . 3 8 30 0 . 1 3 7 6 . 0 8 0 . 3 1 64 1 . 1 9 84.07 1 . 2 1 81 0 . 3 0 101.20 0 . 4 2 98 0 . 3 9 59.53 1 . 2 3 60 4 . 3 4 111.51 4 . 4 5 108
69.41 111.01 119.21 88.28
0.20 0.24 0.27 0.15
86.83 77.54 93.07 78.84
3.51 5.56 4.44 5.73
I
23 99 93 03 02 74 11 46
46 01 83 67 1 24 0 50 0 84 4.65
67.66 105.27 115.43 77.54
0 . 4 3 65.34 0 . 4 7 103.53 0.29 98.88 0 . 2 0 76.96
0.54 0 53 0 42 0.26
81.89 73.33 81.31 61.13
3.90 8.85 4.64 8.66
78.55 63.60 76.23 39.20
4 00 9.71 5.12 9 48
8 2 . 1 8 2 76 94 38 3 57 55 32 8 12
79 86 92 06 49 37
2 97 3 91 9 05
86.97 1 . 7 0 94.96 2 . 7 4 85.96 2.76 115.14 93.80 85.38 100.33 100.91 98.88
1.16 3.39 3.64 3.16 3.56 2.59
95.54 35.57 104.11 109.48 103.96
0.19 82.33 1 . 5 6 33.83 1.11 9 1 . 6 2 0 . 7 1 96.99 0.21 90.31 78.99 81.22
96.85 86.83 75.79 93.94 90.60 89.59
Vol. 21, KO. 12
this size also varies with the material. The increase of cohesion when the moisture content is raised is probably due t o the surface tension of the water films on the particles. Table IV shows the time required for 100 grams of urea and potassium nitrate in the form of 20-30 mesh particles of various shapes to flow from a funnel with a 10-mm. opening. When spherical pellets, granules, and normal crystals of urea were tested in the grain drill attachment in an atmosphere of 40 per cent relative humidity and 68' F., in the manner followed in the previous experiments, the delivery rates were 179, 73, and 44 pounds per acre. Thus it is seen that the delivery rates varied in the same way that the rate of flow varied in the funnel. T a b l e IV-Time R e q u i r e d f o r 100 G r a m s of 20-30 M e s h G r a i n s of D i f f e r e n t S h a p e s t o Flow b y G r a v i t y f r o m a 60° F u n n e l w i t h a 10-mrn. Opening
0 1 1 0
GROCND INTO BROKEN AND CRYSTALS R~~~~~~GRAIXS PELLETS
FERTILIZER Urea Potassium nitrate
0 380 0 225
0 140 0 079
0 231 0 107
1 . 6 4 100.33 1 9 6 3.96 54.65 4 18 5 . 2 7 11.44 6 . 4 4 3 . 3 7 96.12 3 . 6 3 3 . 8 1 89.89 3 . 8 2 2.77 88.86 3.12 0 . 3 1 56.77 3 . 8 3 32.67 1 . 2 0 87.70 0.79 93.51 0.26 85.23 1 . 7 9 56.48 3.03 173.60
0 64 5.48 1.20 0 8i 0 39 3.11 3 41
Undrillable.
formula was derived by which the rate of flow of any comminuted solid may be accurately calculated if the apparent specific gravity, angle of repose, and average size of the particles are known, provided the size of the particles is not less than a certain minimum, which varies with the material and its moisture content. Below this size forces of cohesion become appreciable. Further study has shown that with crystallized ammonium phosphate in equilibrium with 30 per cent relative humidity this minimum size is 125-157 mesh particles, or those with an average diameter of about 0.10 mm. At this size the effect is barely perceptible, but when the size is reduced t o 300-350 mesh no free gravity flow occurs. Increase in water content of the material also increases the minimum particle size that will flow freely and
TEST2
TEST 1 SIZE OF PARTICLES
Mpch . ...
I
First sample
Last sample
First sample
Last sample
Per cent
per cent 26.53 25 17 20 40 11.57 16.32
Per cenl
P e r cenl 10.49 32.40 24.53 15.92 16.66
10.82 15.92 21.02 19.43 32.80
10-20 20-40 40-80
16.31 17.44 20.06 42 3,5
T a b l e 111-Eff e c t of P a r t i c l e Size u p o n R a t e of D i s t r i b u t i o n of M o n o a m m o n i u m P h o s p h a t e a t 68O F. a n d a t Various Relative H u m i d i t i e s RELATIVE HEMIDITY AT680F.
Per cent 40 50 60 70 80
90
1
1
5-10 MESH
Rate per acre
Pounds Pinls 1 0 3 . 2 1 124 103.09 124 100.65 121 9 6 . 9 9 117 8 4 . 0 7 101 8 6 . 5 4 104
I
VJJE
1
tent
Per cent 0.27 0.32 0.41 0.50
0.67 3.07
10-20 MESH R a t e per acre
Pounds 106 85 107.16 105.50 102.80 93 22 88 52
Pints 123 123 121 118 107 102
1 tz:;
20-40 MESH
1
I
40-80 hIESH
80-200 hIESH
Per cent 0.29 0.32 0.43 0.54 0.62 2 76
200
AND
Rate per
'Vater
1
1
I 'y:",'." I tent
acre P n u n d- r . Pints ..
104.98 104.83 101r20 97 28 90 75 71 00
FIXER
125 125 120 116 10s 85
1 Et 1 0.29 0.31 0.42 0.51 0.61 2 97
Pounds 107.40 106.72 102.86 97.43 84 51 29 18
Pints 125 124 120 113 98 34
~
Per cent 0.18 0.20 0.27 0.35 0.41 2.12
1
Pounds 123.49 120.52 113 90 106 71 75 50 11 76
Pints 133 129 122 114 81 13
I
Per Per cent lPounds Pinlsl cent 0.28 0 . 1 7 80 70 115 0.34 0 21 78 99 113 0.46 0 26 75 65 108 0.53 0 33 69 9 8 100 1.49 0 48 17 28 25 1 74 2 10.71 2 51
INDVSTRIAL A.\-D
December, 1929
ENGIAVEERISGCHEIWISTRY
T a b l e VI-Chemical C o m p o s i t i o n of a n 8-12-20 Mixed Fertilizer a8 Delivered a t Intervals f r o m a Fertilizer Distributor SAMPLE
NH3
PzO~
KzO
Per cent
Per cent
P e r cent
8.32 8.27 8.71 8.85 9.31 10.13 9.97
9.14 9.23 9.76 10.06
18.06 19.80 16.70 16.06 14.37 11 39 11 97
10.s1 11.37 12.63
1223
facture by making a slurry of the components to be mixed and graining or spraying them all together. This process probably would not be practical with most present mixtures, but it is feasible with mixtures composed entirely of chemicals. Acknowledgment
In the field this segregation undoubtedly would proceed further than it did in the laboratory, because a machine passing over a tilled field mould shake up its contents more than a distributor running smoothly in the laboratory. This difficulty may be entirely eliminated in the process of manu-
Credit is due W. H. Ross, senior chemist in charge of concentrated fertilizer investigations, and R. B. Gray, 11.A. R. Kelley, and G. A. Cumings, agricultural engineers of the Bureau of Public Roads, for valuable assist,ance in this study. Literature Cited (1) Adams and Merz, I N D . EKG.CHEX.,21, 305 (1929) ( 2 ) Deming and Mehring, I b i d . , 21, 661 (1929). (3) Ross, Mehring, and hierz, I b i d . . 19, 211 (1927).
Biological Purification of Creamery Wastes' Max Levine IOWA EKGIKEERING
EXPERIYEKT STATION
H E rapid growth of the dairy industry and the tendency of creameries to locate in towns rather than on the outskirts of communities has accentuated the problem of waste disposal. At one time agricultural authorities recommended large septic tanks, of about 6 clays' storage capacity, and many such installations may be found, but there is no instance, t o the author's knodedge, where such a device has proved satisfactory. On the contrary, an inspection of several such installations in Iowa disclosed accumulations of precipitated undigested casein and very malodorous effluents. The inadequacy and inefficacy of septic tanks for treatment of creamery wastes as compared with domestic sewage may be readily understood from a consideration of their chemical compositions.
T
Effect of Acidity on Efficiency of Septic Tanks
Domestic sewages rarely show oxygen-consumed values over 90 p. p. m., while the organic and ammonia nitrogen is generally less than 30 p. p. m. Creamery wastes, on the other hand, gave oxygen-consumed values of 600 to 1600 p. p. m. with corresponding nitrogen contents of 40 to 150 p. p. m. S o t only are creamery wastes more concentrated but, what is of considerably greater significance, they are qualitatively different from domestic sewage. The ratio of oxygen consumed to nitrogen is 2 or 3 to 1 for municipal sewage, as compared with over 10 to 1 in the case of creamerv wastes. This high ratio for the industrial waste is due to the presence of lactose, which is practically, if not entirely. absent from domestic sewage. The decomposition of this milk sugar under anaerobic conditions, such as exist in septic or Imhoff tanks, results in the development of high acidities which seriously interfere with septic action. If acid-coagulable substances such as casein are present. these are precipitated. and the septic tank becomes merely a sedimentation or acid-precipitation tank, which rapidly fills, discharging casein and other solids which may soon clog filters. In a paper previously reported ( 2 ) it was shown that digestion of casein and gelatin by proteolytic bacteria from creamery wastes is markedly inhibited by acidify and that it may be completely stopped if the reaction tieconies pH 5.0 to 5.5. Thus a mixture of Flanobacteriunz sitctveolens and Bacterium conzmunior growing aerobically in gdatin for 6 1
Received October 12, 1929.
A N D IOXIrA S T A T E C O L L E G E , A Y E S , I O W A
days produced 855 nig. of ammonia and amino nitrogen and showed a reaction of p H 7.7. In the presence of 0.1 per cent lactose only 329 mg. of ammonia and amino nitrogen were produced, the reaction becoming pH 7.0. Increasing the lactose to 0.2 per cent resulted in a reaction of p H 4.8, with no increase in ammonia or amino nitrogen. As the acidity increased owing to the decomposition of lactose by Bacterium communior, proteolysis by Flavobacterium sztaLieolens was prevented until at p H 4.8 the proteolytic organism in this case was killed. Septic tanks are teeming with lactose-fermenting organisms, so that, if milk wastes enter, the resulting acidities must inevitably interfere with septic action, which is essentially proteolytic. A concentration of about 0.05 per cent milk sugar is sufficient under strictly anaerobic conditions to develop inhibiting acidities. A number of samples of creamery wastes were collected from representative Iowa creameries. The samples were, in each instance, composites of an entire day's run, collected at 30-minute intervals. Of sixteen such samples eight developed germicidal acidities (pH 4.5) and three others markedly inhibitory reaction (pH 5.5 to 5.0) when stored for 2 days at 20" C. The problem of purification of creamery wastes I esoh-eh itself, therefore, into that of devising a mean5 for destroying inilk sugar without the development of detrimental aciditieq. If a creamery located in a city could so treat its waste as to eliminate the acid-producing constituents. the resulting product could safely be added to the municipal sewage. The biological oxidation of sugar under aerobic conditions appeared feasible for such preliminary or partial treatment, and in 1923 (I) it was reported that this could be acconiplished experimentally by the activated sludge process. It way felt, however, that for the small creamery with its fluctuating quantity and variable character of waste, and its limited personnel, the activated sludge process would be impractical but that trickling filters might be feasible and economical. Experimental
Obserrations have been made on the efficiency of trickling filters for the purification of creamery wastes when employing different kinds of filling materials, such as lath, rock, gravel, broken tile, cinders, spiral ring packing, and corncobs. This brief report is restricted to a portion of the ob-
