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T H E J O U R N A L OF INDLTSTRIAL".LVD ENGIYEERING C H E M I S T R Y
Vol. 8, No. 4
EDITORIALS PREPAREDNESS I n all this ebullition of preparedness for defense, there is a t least one prime component which i t is t h e d u t y of every American chemist t o understand. We should not have written this note had we not found by experience t h a t t h e facts are not generally appreciated. We plan a greater navy and a larger army, but we apparently have no assurance t h a t either could be of use in time of war. We are not only failing t o keep our powder dry, b u t we are not even surely planning t o have any powder. It is not generally realized t h a t no useful explosive for a n y military use whatever can be made without nitric acid. From black powder and smokeless, through fulminates, nitroglycerine, dynamite, guncotton, picric acid, t o trinitrotoluol a n d the latest more complex benzol derivatives, not a pound can be made without nitrates. These are now obtained from Chili exclusively. I n the event of any interference with t h a t supply, we should have t o revert t o t h e pea shooter, t h e sling, or t h e air gun. Can we be sure t h a t Chili will always be willing and able t o supply us, and also shall we be able t o transport it in face of foreign opposition of conceivable kinds? These are points which chemists in particular should consider. We have b u t one other considerable source of fixed nitrogen, t h e ammonium sulfate from by-product coke-ovens, a n d this is limited by t h e coke requirements of the iron industry. Carry t h e recovery of this salt as far as possible, as shsuld of course be done in t h e interests of conservation, and t h e supply would still be quite insufficient. Without discussing in detail particular sources of power like t h e Niagara, Tennessee, a n d Columbia Rivers, t h e low-grade coals of t h e culm heaps a n d of certain mines which do not pay for transportation b u t can be utilized on t h e spot, and without referring t o
special processes of nitrogen fixation like t h e arc or cyanamid, i t can be stated with certainty t h a t we have all t h e requisites for a nitrate industry. America has plenty of idle, available power, such as other countries have known enough t o use for this a n d similar purposes, and we have processes capable of economically producing all our needed supply of nitrates, ammonia and nitric acid, while consuming nothing whatever b u t a little of our limitless air and a small part of the wasting energy of some of our moving waters. Furthermore, t h e plant and apparatus for this work can, during times of peace, turn out this same fixed atmospheric nitrogen in the forms which are most demanded by fertilizer requirements. If a manufacturing organization owned t h e farms and t h e water rights, it could and would certainly produce nitrogen fertilizer a t half t h e present cost and would produce explosives with but little added equipment in times of war. This wbuld mean t h a t fertilizers would be used where now, though badly needed, they are prohibitively expensive. Can we not, as a nation, accomplish the same end? I n spite of all the valuable work of improving the yields of corn in such states as Kansas, by breeding t o large grains and big ears, t h e yield per acre is continually a n d rapidly falling off. Wheat yields in t h e northwest have fallen from 40 t o 13 bushels per acre as t h e natural fertilizer has become exhausted. ils this decrease continues, a point will be reached where fertilizers a t any cost will have t o be used. This has been t h e experience of older countries. The time for planning work which takes years t o bear fruit is a t least years before t h e fruit is expected. We need cheaper fertilizers now and we may need our own explosives a t any time. If these words are true, pass them along. If they are not, correct them.
ORIGINAL PAPERS THE REMOVAL OF THE NATURAL IMPURITIES OF COTTON CLOTH BY THE ACTION OF BACTERIA By B. S. LEV~ISE Received January 6, 1916
The ordinary process of bleaching cotton cloth consists of: ( I ) a treatment for t h e removal of certain of t h e natural impurities which may be present; and ( 2 ) a bleaching proper, which decolorizes any impurities left after t h e preliminary treatment. The natural impurities of t h e cotton fibers h a r e been studied b y several investigators with no apparent relation t o t h e processes of purification of cotton cloth, and by t h e writer of this paper in connection with a study of t h e bleaching process. dccording t o t h e results obtained, t h e impurities of cotton fibers can be classified for practical purposes as follows:
1
water-soluble. alcohol-soluble, m i n e r a l , ether-soluble i m p u r i t i e s a n d n i t r o g e n o u s coloring matters. Not all of the above named impurities, as has been shown b y Hebden,' are responsible for t h e yellowing of cloth during t h e steam test or during storage. According t o his opinion, t h e presence of t h e alcoholsoluble and of t h e nitrogenous substances only is responsible for a bleach being imperfect. From a study of t h e ether-soluble, alcohol-soluble and nitrogenous constituents of t h e growing cotton fibers.2 we were able t o corroborate t h e conclusion of Hebden with regard t o t h e significance of the nitrogenous constituents of t h e cotton fibers in bleaching, but our unpublished results of a study of cloth in different stages of t h e bleaching process and of the nature of 1 2
Hebden. THISJOURISAL, 6 (1914), 714. Levine, Sci. N.S., XLI, 1058 (1915). 543-545.
Apr., 1916
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
t h e alcohol-soluble and ether-soluble impurities of cotton showed that the first, contrary t o t h e opinion of Hebden, have no connection with t h e yellowing of cloth, whereas t h e presence of t h e latter. t o which Hel;:ien had ascribed no significance, bears in t h e yellowing of bleached cloth a share fully equal t o t h a t of t h e nitrogenous substances. I n connection with t h e determination of a convenient index of purity of cotton cloth, the question has come up whether t h e present processes of bleaching do not effect any structural differences in t h e cellulose molecule, thus making it possible t o suppose t h a t t h e quality of a bleach might be due t o structural rearrangements. Accordingly, samples of cotton cloth in different stages of bleaching processes obtained from several bleacheries were analyzed for t h e percentages of carbon, hydrogen, a n d of oxygen, a n d tested for their reactivity t o certain chemical reagents. From t h e results obtained, t h e conclusion was drawn t h a t no structural differences were brought about in t h e fiber molecule, a n d t h a t a bleach may be considered t o be “ good,” when all or most of t h e nitrogenous and ether-soluble substances have been removed Thus, it may be said t h a t t h e imfrom t h e fibers. purities which t h e bleaching process is supposed t o remove or decolorize are t h e non-cellulose constituents of t h e cotton fibers, a n d t h a t they are apparently in no chemical union with t h e molecules of t h e fibers. As they are of a n organic nature, it seems possible t h a t they might be rendered soluble b; t h e a-t‘ion of certain enzymes of animal or vegetable origin, and t h a t t h e action of any of these biological agencies upon cotton cloth would result in a n efficient and perhaps cheaper method of purification of fabrics. For some time t h e writer has been engaged in a s t u d y of t h e principles underlying t h e action of different enzyme preparations, of moulds, a n d of bacteria upon t h e impurities of cotton. The present paper deals with t h e study of t h e bacterial treatment of cotton cloth for t h e purpose of removing its impurities preliminary t o bleaching. PRELIIbIIXARY I N V E S T I G A T I O N
The analysis of cloth in different stages of t h e bleaching process and a knowledge of t h e nature of t h e noncellulose constituents of t h e cotton fiber make it clear, as summarily indicated in t h e introduction, t h a t if bacteria are t o be used for t h e purification of t h e cloth preliminary t o bleaching, only those which can bring about all or some of t h e following transformations can be employed: I-Those which render soluble or otherwise removable t h e coagulated non-soluble nitrogen-containing constituents of t h e fibers. 11-Those which render soluble or otherwise removable t h e alkali-resistant waxes a n d t h e fixed fats of t h e fibers which are represented by t h e ether extracts. 111-Those which render easily removable t h e substances which are related t o t h e pectoses. Most of t h e soil bacteria and also some of t h e bacteria which cause certain plant diseases fulfil some
2 99
or all of t h e above conditions. T h e ammonifying and denitrifying bacteria of t h e soil, as is well known a t present, decompose a large amount of organic matter in t h e form of fat, waxes, oils, pectins, gums, and celluloses in order t h a t they may get t h e necessary energy for t h e metabolism of t h e living cell. The bacteria which cause t h e root-rots of certain plants produce strong pectin decomposihg enzymes. The cellulose-destroying bacteria, as was pointed out by Herbert] in 1892, do not attack t h e cellulose molecule proper before t h e pectins, gums, tannins, and other non-cellulose substances have been. utilized by them. Thus, t h e number of bacterial species possessing one or more of t h e properties required for our purpose is very large, and t h e question which arose in connection with our problem was not “ C a n t h e fibers be purified by bacteria,” b u t , ‘(Which species of bacteria shall we employ for t h e solution of our problem? ” T o answer t h e above question a number of bacterial species were secured, some of which were soil bacteria, some intestinal bacteria, and some plant pathogens. These were obtained from t h e collection a t t h e Museum of Natural History in New York, from t h e Vermont Agricultural Experiment Station, a n d some were isolated b y us. I n all cases t h e ident i t y of t h e species was established b y determining their morphological a n d physiological characteristics. The selection of those best suited t o our purpose was made in t h e following way: Flasks of standard broth and of synthetic medium (to be described later) were inoculated with t h e different strains and incubated a t 3 7 . 5 ’ C. from I O t o 14 days. Cotton yarn, which was thoroughly (‘wetted out ’) and sterilized in t h e autoclave, was introduced into t h e flasks and they were again incubated for periods not exceeding I O days. The yarn was then taken out, properly labeled, washed in hot water, and boiled for 5 min. in a I per cent solution of caustic soda. I t was then subjected t o t h e bleach and sour as in t h e ordinary bleaching process, washed, dried, a n d steam-tested. The cultures which gave t h e best results were selected for further experiment. They were t h e following: Bacillus bibulus. , , , , , ,-, , , Bacillus carofovorus,, , , . . Bacillus sublilis (Ehrenberg) . .,. . . . . .
.
... . . ..
,
..
Cohn
All these bacterial species produce enzymes by means of which they’ perform t h e transformation of such substances as sugars, starches, gums, pectins, celluloses, and various proteins into substances, t h e molecules of which are much smaller t h a n and possess chemical properties differing from those of t h e original substances, so t h a t they can be easily distinguished from them. Thus t h e starches are broken down t o dextrins and t o dextrose, t h e pectins are changed t o pectic acid, t h e celluloses t o carbon dioxide, methane, various organic acids, and water. The proteins are broken down to carbon dioxide, water, ammonia, nitric a n d nitrous oxides, free nitrogen, and perhaps some other compounds. These bacterial enzymes 1
Ann. Agrow , 18 (1892), 536-550.
T H E J O G R N A L O F I N D L - S T R I A L AArD E N G I N E E R I N G C H E M I S T R Y
3 00
diffuse in t h e surrounding media t o a n extent which depends upon t h e amount and diffusibility of t h e enzyme produced. Hence, from the amount of substrate transformed, t h e enzymic strength of t h e bacteria may be determined b y plating t h e bacteria o u t on agar containing a known per cent of t h e substrate and incubating for a few days. The enzyme excreted b y the organism usually diffuses equally in all directions, and t h e circular zones around t h e colonies may be made visible b y treating the plates with suitable reagents. The diameter of t h e circle can be measured and compared with t h a t of zones produced b y other organisms on t h e same substrate and their relative efficiency may thus be ascertained. The zone formed b y a bacterial colony has been called t h e “enzymic zone” and its diameter expressed in millimeters or fractions thereof. T o further test t h e suitability of t h e strains previously selected. t h e bacteria were grown on celluloseagar plates, starch-agar plates, pectin-agar plates, and their enzymic zones measured. The starchand t h e cellulose-agar were prepared as follows: CELLULOSE-AGAR STARCH-AGAR Cellulose Solution Starch Solution Nutrient Solution Nutrient Solution Agar Agar
PECTIN-AGAR Pectin Solution Nutrient Solution Agar
AMOLXTS 500 cc. 500 cc. 10 g.
T h e cellulose and the starch solutions were made u p according t o t h e directions given in Bulletiz 266, United States Department of Agriculture, Bureau of Plant Industry, page 28. The pectin solution was so. A I . .. . .
,
.,..
A * . ,. . . . , . . . A3 . . . . . , . . . An,, , . . , . . . , 45.. . . , . . . .
CULTURE B. amylolytirus B. bihulus B. $mi B . carotowrus B. suhtili..
CULTURE B1,. , , , . . , . B. amylolyticus Bz ..... , . , , B. hibulus B3 ,.... . . . . , B. jimi Bd, ., . . . . . , B. carotoaorus B5 .... , , , , , B. subidis
NO.
No. C1 C2 C3 CI Cj
1701.
8 , NO. 4
Eh-zYhrIC ZONES
STARCH B. hibulus.. , . , . , , , , , 1.0 t o 2.0 mm. B. $ m i . . . . . . . . . . . . . . . . 2.0 t o 3.0 mm. B. amylolyticus.. , . . . . . 0.5 t o 1.0 mm. B. carotoziorus.. . . . . . . . . 1.5 t o 2.0 mm. B . suhlilis.. . . . . . , . , . , , ?
..
1
CELLULOSE 0.1 t o 0.3 mm. 0.5 t o 1.0 mm. 0.5 t o 1.0 m m . ? 0.2 t o 0.5 mm.
PECTIX 1.0 t o 1.5 mm. 0.5 t o 1.0 mm. ? 1.5 t o 2.5 mm. 0.7 t o 2.0 mm.
I t may be seen from a n examination of this’ table t h a t t h e transforming strength of t h e enzymes produced by t h e bacterial strains selected was great in all cases, and t h a t their suitability t o our work, as determined b y t h e previously described flask-incubation method. was confirmed ACTION O F BACTERIA U P O X T H E I N P U R I T I E S OF
C O T T O P ; CLOTH
The bacterial strains selected as previously described were employed further in t h e study of t h e action of their enzymes upon t h e impurities of cotton cloth. Five hundred cc. of the nutrient solution described above and j o g. of coarse cotton cloth containing about j per cent b y 17eight of starch as a “sizing” material were p u t in each of 1 5 flasks a n d sterilized in t h e autoclave for 30 min. Sets of 3 flasks were then inoculated with t h e liquid cultures of t h e bacteria employed and incubated a t 3 7 . j ” C. Control flasks with t h e nutrient solution and cloth were sterilized as described above and incubated without having been inoculated. One sample from each of t h e cultures was t h e n taken out I mo., 2 mo., and 3 mo. after inoculation. The samples were thproughly washed in boiling water t o remove all t h e solu-
TABLE I-TESTS OF CLOTHSAWPLES AFTER 1 MONTH’SINCCBATIOX Starch Test Transformation t o a Dextrin Softening of Cloth Violet-blue Slight Violet Less t h a n AI Greenish Considerable Greenish Decided Considerable Greenish violet Less t h a n above Moderate
Condition of “Motes” Merelv swollen Swofiznand-slightly discolored Swollen and slightly discolored Swollen and slightly discolored Swollen and discolored
TABLE 11-TESTS OF CLOTHSAMPLES AFTER 2 Starch Test Change beyond 1 Mo. Condition Violet h-ot marked Marked Greenish Decided Light green Light green Decided S o t marked Greenish violet
Condition of “Motes” Same as -41 Almost completely gone Barely colored and partly gone Swollen and slightly discolored Swollen and slightly discolored
MONTHS’INCUBATION Softening of Cloth More t h a n AI Much more t h a n A2 Much Moderate Slight
T.4BI.E 111-TESTS OF CLOTH SAMPLES AFTER 3 MONTHS’I K C U B A T I O X Softening Strength BLEACHEDSAMPLES(U) CULTURE Starch Test Starch Transformation Indicated of Cloth of Cloth Condition of “Motes” COLOR MOTES B. amylolyticus Faint violet Partial removal of amylodextrins Considerable Unimpaired Strongly discolored White Sone Very white None B. bihslus Very faint green Change or solution of dextrins Decided(h) Weakened(c) Mostly gone Whitest of all S o n e B. $ m i Negative Changed t o sugars o r achrodextrins Decided(d) Impaired(c) Mostly gone Very white Sone B. carotovovus Very light green Removal of dextrins Considerahle Unimpaired Mostly gone B.sublilis Violet (greenish) Further change in amylodextrins Some Unimpaired Swollen and discolored White Sone ( a ) See text for method of bleaching. ( h ) Pinkish tint. ( c ) Signs of disintegration where t h e cloth was not wholly submerged and came in contact with t h e air. ( d ) Pink t i n t lighter t h a n C2.
prepared from t h e water-soluble substances of cotton in t h e following way: Unspun non-absorbent cotton was percolated with water for 24 hrs., t h e cotton pressed out and the solution filtered t o clearness; it was then evaporated t o dryness on a steam b a t h , and I O g. of the dried extract were dissolved in j o o cc. of water. The nutrient solution consisted of I g. each of dibasic potassium phosphate and magnesium sulfate, 2 g. each of sodium chloride. ammonium sulfate and calcium hydrate, and 1000 cc. of water. T h e bacteria mere plated out on each of t h e media described and incubated a t 3 7 j o C. in a chamber saturated with moisture so as t o prevent drying of t h e plates. After I O t o 14 days’ incubation, t h e enzymic zones were measured. The results were as follows:
ble products of the bacterial metabolism and t h e adhering chemical reagents of the medium, and t h e samples taken from t h e flasks incubated for I and z mo. were tested for starch; t h e samples taken from the flasks incubated for 3 mo. were tested for starch, nitrogen, and ether- and alcohol-soluble substances. The strength of the cloth, its softness, and the disappearance of t h e “ m o t e s ” were also noted. The results appear in Tables I , I 1 and I11 Samples from all t h e 3-mo. incubations were bleached for 41/2 hrs. in a solution of freshly prepared calcium hypochlorite of 2’ Tu: They were then thoroughly washed in cold water and p u t into a solution of sodium bisulfite (4’ Tw.) €or another 41jz-hr. period. d f t e r this, t h e cloth was thoroughly washed, dried, ironed,
T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G C H E 2141S T R Y
Apr., 1916
I
and compared as t o whiteness, with t h e results noted in t h e last two columns of Table 111. The bleached samples were then subjected t o t h e steam test under a pressure of I O lbs. per sq. in. for 4 j mins. None of t h e samples were yellowed b y such treatment, and we assumed, therefore, t h a t all t h e substances which cause yellowing of t h e bleached cloth during steaming or during storage were removed. I n order t o determine whether t h e removed substances were t h e same as determined b y t h e analysis of cloth in t h e different stages of t h e bleaching process, the bleached samples from t h e bacterial treatments were analyzed for the determination of t h e percentages of t h e ether-soluble, alcohol-soluble, and nitrogencontaining substances which were left in or on t h e fibers after t h e “chemick” and the “sour.” T h e results are given in Table IV. The cloth incubated in t h e control flasks after the 3mo. incubation showed no starch transformation. very slight reduction in t h e percentage of t h e ethersoluble and nitrogen-containing substances, and no change in t h e percentage of t h e alcohol-soluble substances. I n all t h e bacterial treatments, t h e nitrogen-containing substances were removed from t h e cloth completely, t h e ether-soluble substances were removed
.
The transformation of nitrogenous substances which is usual in t h e case of decomposition of organic matter in t h e soil, suggests a way in which t h e answer might be given. T o determine whether t h e case in our experiment was similar t o t h a t of t h e above mentioned condition in t h e soil. we tested several samples of media, taken out a t various times of incubation, for t h e presence of ammonia. The quantity of cloth and t h e small percentage of t h e nitrogenous substances in it rendered our attempts fruitless. We were about t o give u p further investigation along t h a t line, when we found in some of the flasks a very slight, white precipitate. On testing, it proved t o be calcium carbonate, and it a t once occurred t o us t h a t in t h e presence of calcium hydroxide t h e decomposition of t h e nitrogen-containing substances may be accompanied by t h e formation of calcium carbonate. free nitrogen or ammonia. and water. The nitrogenous coloring substances. of cotton in t h e American and t h e Egyptian varieties were studied by Dr. Schunk,’ and according t o his analysis t h e formula for t h e substances found in t h e American variety would be CI0HI204N,and t h a t of the substances found in t h e Egyptian variety C2jH3009N3. I n t h e presence of calcium hydroxide t h e reactions brought about during t h e decomposition of t h e first
TABLE IV-TESTS SHOWING REMOVAL OF IMPURITIES FROM CLOTHSAMPLES BY INCUBATION FOR 3 MONTHS A N D SUBSEQUENT BLEACHING NITROGEN (OR PROTRIN) ETHERE X T R A C T ALCOHOLEXTRACT PER CENT PER CENT P E R CENT GRAMSGRAMS AFTBR REMOVED BY GRAMSGRAMSA F T E R REXOVED BY GRAMSGRAMS AFTER REMOVED BY
ORIG- Incubation INAL B. amrlolrticus. 0 . 1 5 6 0.0032 B. bibulus.. . . . . 0 . 1 5 6 Trace B . f i m i. . . . . . . . 0 . 1 5 6 0 . 0 3 8 B. carotovorus.. 0.156 0 . 0 2 5 B. subtilis . . . . 0 156 0 . 0 1 2 CULTURE
.
Incu“Sour” bation “Sour” None 75.8 24.2 None 100.0 None 97.9 2:l None 84.4 15.6 None 92.9 7.1
Total 100.0 100 0 l00:O 100.0 100.0
ORIG- IncuIncuINAL bation “Sour” bation “Sour” 0 , 3 9 2 0.059 0 . 0 1 5 7 8 . 8 9.3 0 . 3 9 2 0.0716 0.0446 7 8 . 6 9.3 0.3920.117 0.041 85.0 11.2 0.392 0.075 0.039 8 0 . 9 9.1 0 , 3 9 2 0.125 0.079 6 8 . 1 1 1 . 2
more efficiently t h a n they were after t h e chemical process of bleaching, the alcohol-soluble substances remained unchanged, except in t h e case of t h e cloth subjected t o t h e action of cultures of B . carotovorus a n d of B. subtilis. The weakening of t h e cloth in t h e samples subjected t o t h e action of cultures of B . bibulus a n d of B . $mi may have been due t o t h e action of t h e oxygen of t h e air on those parts of t h e cloth saturated with t h e calcium hydroxide of t h e media which were not completely submerged. It is possible also t h a t during t h e long period of incubation t o which t h e cloth was subjected, t h e bacteria may have acted upon i t t o such a n extent t h a t a slight general disintegration was caused. But as t h e reactivity of t h e cloth remained apparently unchanged, we feel safe in concluding t h a t a more thorough investigation of t h e action of some of t h e bacteria upon t h e impurities of cotton cloth would determine t h e conditions under which t h e bacteria would remove t h e nitrogenous and ether-soluble substances of t h e fibers without impairing t h e body of t h e fabric. THEORETICAL CONSIDERATIONS
The question may be asked in connection with t h e disappearance of t h e insoluble nitrogen-containing substances of t h e cotton fibers: “How have they been removed t o such a n extent by t h e action of bacteria?”
Total 88.1 87.9 95.2 90.0 79.3
ORIG- IncuINAL bation “Sour” 0.5107 0.5107 0.4569 0.5107 0.5107 0 . 4 7 2 0.51070.51070.4098 0.5107 0 . 3 2 3 0.306 0.5107 0 . 4 6 5 0.457
Incubation 0.0 0.0 0.0 35.9 8.9
“Sour” 3.2 3.0 2.5 5.2 2.5
Total 3.2 3.0 2.5 41.1 11.4
b y means of oxidation may be represented by t h e following equations: 4CI0H1204N 40Ca(OH)? 4102 = 4oCaC03 4NH3 j8H20 2CloH12O4N 2oCa(OH)2 ZZOZ = zoCaCOs 32Hz0 NZ a n d for t h e oxidation of t h e latter in t h e presence of calcium hydroxide t h e reactions may be represented as follows: 4 C 2 S H 3 ~ 0 9 N 3 IooCa(0H)z 10302 = 1ooCaCO3 12”) 142H20 2Cy6H3009N3 5oCa(OH)2 j602 = 5oCaC03 80H20 3x2 Free ammonia and free nitrogen are thus formed which could not be detected by us on account of t,heir small amounts. As there was no precipitate found in some of t h e flasks, it may be supposed t h a t mere liquefaction of t h e protein substances took place which rendered possible their complete removal after t h e strong oxidation during t h e “chemick” which had most probably converted the peptones and amino acids formed into nitrates and nitrites. The reactions just given are of t h e nature of oxidations and result in liberation of energy. It therefore seems probable t h a t t h e nitrogenous substances of t h e cotton fibers form some sources of energy t o t h e
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1 Memoirs, Manchester Literary and Philosophical Society, Vol. IV, 3rd Series.
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bacteria. T h e pectins, gums, and waxes, no doubt, are used up b y t h e m first, t h e nitrogen-containing substances next, and, as t h e medium used in our experiments was devoid of carbohydrates, t h e cellulose finally was drawn upon b y t h e bacteria as a source of energy. This probably would not be t h e case in t h e practical application of bacteria t o t h e treatment of cotton cloth before bleaching, as t h e period of incubation would have t o he reduced to a minimum. T h e weakening of t h e cloth would be eliminated entirely. and a cheaper, safer, and more convenient process for t h e purification of cotton cloth preliminary t o its bleaching would t h u s be obtained. Since t h e conclusion of t h e above described preliminary experimental investigations, studies have hecn carried on with a view t o applying bacteria t o practical purification of various cellulose fibers. By using different combinations of bacterial species, different media, different reactions of the media t o s t a r t with, and different temperatures during the period of incubation, t h e latter was reduced t o 7 2 , 48, 3 6 , and in some cases even t o 24 hrs., all depending upon t h e nature of t h e fibers used. A number of tests on a large scale were also performed for t h e purification of paper-making stock in connection with one of t h e eastern paper making factories, and for t h e purification of cotton yarn and cotton cloth in connection with some of t h e Rhode Island bleacheries. I n all cases t h e results obtained were very encouraging.
Vol. 8 ,
KO.4
VI-Bacteria may bc profitably employed :LS a substitute for t h e present method of purifying cloth preliminary to its bleaching. T h e present paper records a part of the work done by the author along similar lines for Mr. J. .:I Hehden of Providence, R . I., in connection with ;ind under the auspices of t h e Biological Laboratory of Brown University. T h e author wishes t o express his gratitude t o the instructing staff of t h e Brown University Biological Laboratory and t o 11r. Hebden for their general and generous assistance in the work and for permission t o publish the results. BIOLOCICAI. Lneoa~ro~u. BROWN Faovsm!~cl;. R . I.
UNIVERSITY
PHYSICAL PROPERTIES OF DENTAL CEMENTS RY P*U'
POBT.CHBB
Receivcd Decembrr 2 2 . I l l 5
The principal types of dental cement which occupy a useful place in dentistry ?t t h e present time are known technically as t h e silicate, zinc oxyphosphate and copper cements. All of these products reach the dentist in t h e form of a powder a n d liquid to be combined, as occasion requires, by a special process of mixing. The constituents and applicatioris of t h e three types and the various properties upon which their uses in applied dentistry depend. arc given in Table I. I n order t o determine thc "filncss" of :L dental
SUMMARY
I-Of
all t h e natural impurities of cotton cloth only t h e nitrogencontaining and t h e ether-soluble substances, when insufficiently removed from t h e cloth previously t o t h e "chemick," cause yellowing of bleached cloth in the steam test or during storage. 11-The nitrogenous substances of t h e fibers were broken down b y bacteria so t h a t they were completely removed from t h e cloth. This transformation in t h e presence of the calcium hydroxide has probably resulted in some cases in t h e formation of either free ammonia or nitrogen, calcium carbonate, and water, and in some in the reduction of the nitrogenous substances t o peptones and amino acids which are easily oxidized t o nitratcs a n d nitrites. 111-The ether-solublc suhstances of t h e cloth were removed in our experiments by bactekial . t r e a t m e n t more efficiently than is the case in t h e ordinary bleaching process. IV-The alcohol-soluble substances were very little attacked by t h e bacteria, probably because of t h e formation of a calcium salt in t h e presence of t h e calcium hydroxide of t h e media. V-Sone of t h e bacteria experimented with havc transformed the starch of thc cloth any further than to dextrins.
cement, due consideration must be givcn t o its various properties, individually and collectively. A silicate cemcnt which does not possess t h c required color and translucency would he lacking in the essential requirements of this typc of cemcnt. and no mattcr how perfect in other respects, it would fail to fulfil its main p u r p o s e i t s ability t o match the tooth structure in appearance. Likewise. germicidal efficiency is essential in a copper cement. I t is obvious t h a t
