October, 1!72;,
INDUSTIZIAL A N D KVGINEEEING CHEMISTRY
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Smoke Cloud from 100-Pound Whlle Phusphurua Airplane Urop Bomb
Screening Smokes’* By 11. W. Walker CIIIIMICAL Wanwnxs SEXVICB. Encrwoun ARSENAL, M u
HE masking of movements of attacking troops is probably as old as the art of narfare. Taking advantage of natural cover or darkness to surprise the enemy, or to concral the direction of an attack, was fundumental ihmvledge, ever1 among savages. Artifirial means of this hind data b;zk at least as far as the use of the wooden horse iege of Troy. Shakespeare clcscribcs artificial masking of t,he advance of arr army in “Macheth,” where “Great I+irlram Wood moved to high Dunsiirame Hill,’’ each man mt,ting down the bough of a tree am1 carrying it before him i,) “shadow the numbers of our host, and make discovery w r iii report of us.” Smokc screens had beeii used to more or less advantage iir minor navul operations a t least as far bnek as the Civil \Var, when blockade runners, to cvade piirmit, took advantage of dense black smoke produced by using wood high in pitch and resin as fuel for the boilers. But iio large-scale intelligent use of screening smokes was made by military forces prior to the World War, when its importance, both as im offensive and a defensive factor, was definitely established.
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Theoretical Definition and Properties of Smoke Screens
A smoke screen consists of a cloud of liquid or solid particles in a very fine state of subdivision between the observer Received March 26, 1926. *Published by permission of Chief, Chemical Warfare Service. I
snd the ob,iect, in sufficient concentration to obscure the object completely from the observer. The screeiiirig eRect of different smoke materials is p&ably proportimil to the qua1rtit.y of material between the eyc and the object, provided the materials are in the sane relat,ive state of subdivision and, if the tcrm “volmne” ire 3ubstit.ntod for “quantity,” the screeiring effect is prolmbly directly proportional to the total volume of all the partiolei betweerr the eye a i d the object, regardlcss of the material, if it iu assumed that the material is in the same state of SU~Jdivision. As a matter of fact, the bulk of visible particles which go to make up a smoke cloud are of the order of from 10-4 to 10-j em. in diameter, and under the average field conditions the particles could he considered of the same degree of subdivision withoirt the probability of very great crror. Note-The blindiiig effect of light superimposed upon the eye by reBeetion irom whit.e rloiid~has always been supposed to make W h i t e smokes mom effective than black smokees, but no qlrantitative data hsve heen available on this point. Experiments hre now under wey which will determine quantitatively the relative eajcieocy o i white. black, nud intermediate cobred smokes.
The material between the eye and the object is irsually different in its chemical composition from the original compound in that it has combined with one or more of the coristituents of the air. Thus, in the case of phosphorus, phosphorus pentoxide is formed first and then phosphoric acid, or in other words, one pound of phosphorus combines vith the oxygen and water vapor from the air to produce 3.16 pounds
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Vol. 17, No. 10
of phosphoric acid, and this phosphoric acid takes up still both velocity and direction, K is in the neighborhood of 10, more water vapor to make a dilute solution of phosphoric acid and H in yards per minute = 1Odv. in the form of minute droplets, which particles or droplets Outside of the general effect on K, the lateral spread is of of dilute phosphoric acid are the actual screening material. importance only in the case of frontal screens-that is, The same number of the same-sized droplets of a dilute solu- screens in which the direction of the wind is either on a line tion of sulfuric acid, or of any other solution which produces from the observer to the object, or vice versa. The lateral a white, or nearly white, smoke, will.probably give obscurance spread of the cloud a t any given distance from the source, equal to that given by the phosphoric acid droplets, but the provided the wind is fairly uniform in direction, is approxiinitial amount of sulfur trioxide, or oleum, necessary for the mately equal to twice the vertical rise, or the lateral spread production of sulfuric acid solution droplets, is greater than the initial amount of phosphorus required to produce the same in yards per minute = 2 H = 2 O c V . Although so far there is no direct evidence to prove it, bulk of phosphoric acid droplets. general observation seems to indicate that there is no gradual It does not necessarily matter whether or not the particles absorb, reflect, or refract the light, so long as the object is decrease of concentration towards the edge of a smoke cloudscreened, but it is believed that by far the greatest factor is rather, there is a sharp transition from a high concentration the actual blocking of the light rays by the particles in line in the cloud to a zero concentration of the smoke just outr side the cloud. This is based on the fact that clouds in genwith the object. It follows that if there is a sufficient volume of smoke par- eral show sharp, distinct edges and that a person near a cloud ticles between the eye and the object to obscure the object, in a steady wind can be either in the cloud or just outside it. it makes no difference whether this volume of particles is These and other observations seem to indicate that a t a highly concentrated in a comparatively small depth, or is given distance from the source the average concentration of spread out along the entire distance between the eye and the smoke throughout a cloud generated from a single source is object. This has been borne out by experimental data, and fairly uniform, regardless of whether the sample is taken these data, in fact, indicate that possibly greater obscurance near the edge, in the middle, or near the top of the cloud, is obtained by spreading the same volume of particles over provided, of course, that the distance from the source is the a greater depth than by confining them in comparatively same. It is hoped in the near future definitely to prove or disprove this assumption by actual analysis of samples. narrow limits. I n the case of practically all substances being considered It is evident from the foregoing that the decrease in concenfor military smoke screens, the particles of actual smoke- tration or density of a smoke cloud is proportional to the where C is the concenproducing material are liquid. I n the case of destroyer square of the distance or C = K/D2, smoke screens used by the Navy, the actual smoke-producing tration, K a constant, and D the distance from the source in material is probably a combination of liquid particles of oil yards. In addition to the concentration data desired above, it is and moisture and solid particles of finely divided carbon. hoped that analysis of samples of various smoke materials will give an exact idea of the amounts of water vapor that are Cloud Travel taken up from the air by various smoke agents under varying Inasmuch as smoke is carried with the wind, in order to conditions. screen any objective for a given period of time it is necessary Properties of Ideal Smoke-Producing Material to generate smoke continuously for the desired length of time The ideal agent for screening smokes should produce a from a source which may be either a point or a front. It naturally follows that it is necessary to understand the funda- maximum volume of actual screening material for a minimental mathematics of smoke cloud travel. Observations mum original weight. Its characteristics should be such that of a great many clouds indicate that the resultant of the upper the rate of smoke production can be readily controlled, and boundary of a smoke cloud is a straight line for a t least the little or no heat should be evolved in the formation of the first 600 yards of its travel and the available data on longer final obscuring product. It should be nontoxic and nonclouds indicate that this straight line effect continues for irritating. It is obvious that it should be readily available practically the life of the cloud. It is true that there is a and commercially economical, and should not be dangerous small initial rise in the first few yards, due to the initial ther- t o handle. If it were possible and practical, probably the ideal smoke mal effect of smoke generation, but what evidence there is s e a s to prove that this effect is dissipated before the cloud screen would be one in which the cloud was manufactured by has traveled a hundred yards. It is also true that the smoke the catalytic change of the water vapor in the air to parcloud travels at approximately the same speed as the wind, ticulate droplets, especially if a mobile catalyst could be and that the resultants of the lateral edges of the cloud may devised which could perform this phenomenon in any parbe considered straight lines. I n other words, the cloud ticularly desired area or locality. Failing this, if a method spreads more or less uniformly both upwards and sideways could be devised for the catalytic oxidation and synthesis of as it travels along. The main causes of this spread me the sulfur to minute droplets of a dilute solution of sulfuric acid, turbulence of the atmosphere and the character of the using the oxygen and water vapor of the air, it would probably terrain. The turbulence of the atmosphere seems to be a be a more economical and practical smoke than white phosfunction of the wind velocity, and it has been shown that for phorus. The possible atomization of water into minute droplets any given wind velocity the rise per minute of the cloud is and 10-6 cm. in diameter, by forcing through approximately equal to a constant times the square root of of between the wind velocity in miles per hour, or H = K d V . This a nozzle or by any other means, might produce screens very constant is really made up of two variables and a constant, economically and efficiently. the variables both being functions of the wind velocity. Methods of Smoke Generation One, called the “gustiness” factor, is obtained by dividing Thwe are three general classes of dispersion, all of which are the average wind velocity by the maximum variation of the velocity and adding one; the other is an arbitrary factor used to some extent in the production of screening smokes. based on the changes in direction of the wind during the gen- and require chemical or physical change before the final eration of the smoke cloud. If the wind is fairly steady in obscuring product is formed:
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October, 1925
e n f r o m Whlte Burned i n Pans
H. C . Candle S m o k e Screen
oxide reacts with the water (1) E x p l o s i o e . T h i s vapor in the air to produce method includes the disperfine droplets of sulfuric acid, sion of smoke by artillery which combines with still shell, Stokes mortars, Livens projectors, hand and rifle more water vapor to form grenades, and drop bombs. droplets of a dilute solution The smoke material is loaded of sulfuric acid, which is the in the projectile and dispersed ultimate screening material. by an explosive charge set off Seither sulfur trioxide nor by means of a time or impact fuse oleum is harmful to man in ( 2 ) Thermal. In thisclass ordinary concentrationsis included the production of Cloud from Burst of 4 - I n c h White Phosphorus S t o k e s Shell although they are somesmoke screens by means of what irritating-and both candles, airplane exhaust, smoke boxes, the stacks of destroyers, etc. The general principle is are readily available on a large scale commercially, can that the original material is converted by means of heat into a be ,+.tored in iron or steel containers, and are economical in form whereby it acts chemically and physically with the constituents of the air to produce the final obscuring product. price. The only use for pure sulfur trioxide is in shell or (3) Pressure. This method of smoke production includes the bombs, but oleum can also be used as a spray in the exhaust use of oleum, titanium tetrachloride, and tin tetrachloride re- of airplanes-although it is quite injurious to the present airleased from cylinders, the navy smoke funnel, and similar appli- plane tanks and destroyers, and may possibly ances. Usually the agent is placed in the cylinder under prescurtains. sure and upon being released through an atomizing nozzle passes be used in through the vapor phase and is condensed in the form of small Titanium Tetrachloride particles, which react with the constituents of the air to a greater or less degree, depending upon the specific properties of the maThis material is a liquid boiling a t l%' which, when terial. I n the case of the navy smoke funnel type, two materials are stored in cylinders under pressure and released simultaneously released under pressure through a nozzle, forms a a hydrate, t o combine chemically to form a compound which reacts with the TiC14.jH20,with the \yater vapor in the air, which upon furconstituents of the air to form the final obscuring product. ther reaction with moisture breaks up into titanium hydToxide
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Present Materials Considered for Screening Smokes White phosphorus is a solid, melting a t 4 4 O e. and boiling at 2900 c.,which oxidizes upon contact with air a t ordinary temperatures, or upon burning in air, to form phosphorus pentoxide, which takes UP water vapor to forin phosphoric acid, and this phosphoric acid absorbs still more water vapor from the air to form a dilute solution of phosphoric acid. One pound of phosphorus produces 3.16 pounds of phosphoric acid. It is commercially available in large quantities and is comparatively reasonable in price. It is used in shell, stokes bombs, grenades, drop bombs, and attempts are being made to use I t in a candle. It is not corrosive when sealed in iron or steel containers, and the smoke produced under field conditions is not injurious to men or equipment.
and hydrochloric acid. Under conditions of high humidity this hydrochloric acid condenses with water to form minute droplets of dilute hydrochloric acid solution. Titanium tetrachloride smokes dissipate more quickly than either phosphorus or oleum smokes, even under conditions of high humidity, possibly due to the difference in vapor pressure of solutions of hydrochloric acid as compared with phosphoric acid or sulfuric acid. The smoke produced is not injurious to man under ordinary conditions, and is only slightly irritating. The liquid titanium tetrachloride is corrosive to fabrics and the human skin, and is highly injurious to untreated airplane fabric. Titanium tetrachloride is not now available in large quantities commercially and is comparatiyely expensive. Although the smoke is considerably inferior to white phosphorus or oleum in shell and bombs, it is used a t preserlt in the airplane exhaust smoke and the airplane curtain because it is the most desirable for that purpose.
Sulfur Trioxide and Oleum
Silicon Tetrachloride, Ammonia, and Water
Oleum is ~b solution of sulfur trioxide in sulfuric acid. Sulfur trioxide exists in two forms, the ordinary stable one which would be used for chemical warfare work being the beta modification, which melts at 50" C. The sulfur tri-
The proportions that give the best results are 2 of silicon tetrachloride to 1 of ammonia by weight. This smoke is generated from a smoke funnel. One cylinder is charged with silicon tetrachloride containing about 10 per cent carbon
White Phosphorus
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INDCSTRIA L A N D BNGINEERING CHEMISTRY
dioxide under a maximum pressure of 550 pounds per square inch at 55" C. The other cylinder contains liquid ammonia. Upon discharging t,he cylinders the silicon tetrachloride and the ammonia react to form ammonium chloride, which probably takes up water vapor from the air to form the screening product. The smoke produced is harmless and stable. Ammonia is now commercially available in large quantities, and silicon tetrachloride could readily he obtained in large quantities if there were sufficient demand. These materials are used in the navy smoke funnel and the smoke knapsack B. M. Mixture and H. C. Mixture
The B. M.mixture consisted of zinc dust and carbon tetrachloride along with relatively small percentages of ammonium chloride, sodium chlorate, and magnesium carbonate. This mixture proved unstable on storage and the present H. C. mixture was evolved. The main difference in this mixture is that solid hexachloroethane is used in place of the liquid carbon tetrachloride as the chlorine carrier. This mixture is stable on storage. Tho smoke produced is the product of the zinc cliloride with the water vapor in the air. The product is harmless and is not irritating in low concentrations, hut causes conghing and throat irritation as the concentration increases. The mixtiire is safe and easily handled, but the cost is comparatively high, although either the 11. C . or the B. X I . mixture could be supplied on a large-scale basis. I n case of war, when long-time storage would not he necessary, the B. M. mixture might prove more economical. These mixtures are used in candles, the 4-inch Stokes mortar shell (burning type), and I$. C. grenades. Crude Oil
A dense, dark smoke screen can be set up by destroyers by spraying oil below the stack with an insufficient supply of air. The smoke itself probably consists of particles of carbon and some tarry and oily matter, augmented by films of condensed water vapor. This method of smoke production ciits down the speed of the destroyer and fouls the boiler tubes, but it is probably one of the most economical nrethods for the production of naval screens by destroyers. The smoke is harmless, but soils everything with which it comes in contact.. The smoke-producing material is always available, being part of tire fuel supply necessary for the propul,
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sion of the vessel. At the present time no feasible method of using crude oil screens on land has been found, and its use is limited to large-scale naval screens. Other Materials
The above-mentioned materials are the main sources of smoke production now being considered. The disadvantages of such materials as tin tetrachloride, chlorosulfonic acid, ammonia and hydrochloric acid, the British Type S mixture, etc., are such that no real use will be made of them unless some new development in the method of t.heir use be discovered. Summary
Crude oil, oleum, and phosphorus will give maximum obscuring power at minimum cost, in the order named. For obscuriiig power for a given weight of material, the order is just reversed, and wlieri it is remembered that the use of smoke at the front depends upon t.he total cost of the weapon, its use, its efficiency, its transportability and other factors, as well as the original cost of the smoke agent, i t is likely that phosphorus, sulfur trioxide or oleum, and crude oil will he the three smoke agents of general use, except in the case of airphne distribution.
Tactical Use of Smoke Briefly stated, the essential of an efficient smoke screen is that it must give the desired obscuring effect for the total front or object to be screened from all enemy points of observation for the desired duration of the screen, with minimum impedance to one's own observation, artillery fire, and general communications. This necessitates a thorough knowledge of all phases of the situation by the gas officer, who must determine whether or not these conditions can be met by use of the material on hand under the prevailing weather conditions. Knowing the kind and quantity of smoke agents on hand, and the weather conditions, he should be able to determine how large and how effective a screen can be established a t a given locality, and haw long it can he maintained. It naturally follows that he must make the choice of method for establishing and maintaining t.he screen and, according to the situation, should decide whether artillery, Stokes, Livens, candles, airplanes, or other devices should be used.
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I I Smoke Screen from SO-Pound White Phosphorus Candle
October, 1925
INDCSTRIAL A N D ENGINEERING CHEMISTRY Airplane Possibilities
The development of the airplane exhaust and curtain smokes since the war has opened up new possibilities in putting down much more effective screens a t points that were hitherto more or less inaccessible for good screens and a study of airplane smoke tactics constitutes a field in itself. Naval Possibilities
Especially is this so in naval warfare, where previously screens had to be maintained by the use of an excessive amount of smoke for a very long period to enable destroyers
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to attack successfully. By use of airplanes, effective and economical screens can be established for any desired sea area, and the screen can be originated comparatively close to the target or object, instead of five miles or more away, as was previously necessary. I n addition to screening torpedo attacks by destroyers, these screens can be used to block out part of the enemy fleet, making possible a concentration of fire on almost any desired number of enemy ships a t a cost of very little material, and the probability of loss of airplanes would be much less than the probability of loss of one or more destroyers engaged in setting up such a screen.
The Manufacture of Pectin’ By C. P. Wilson RESEARCH LABORATORY. CALIFORNIA FRUITGROWERS EXCHANGE, SAX DIMAS,CALIF.
Although it is customary to boil fruit juices to obtain a ECTIN was discovered in 1825 by Braconnot,2n*who made artificial jellies with pectin obtained from proper concentration to produce a jelly, it has long been recogcarrots. Since then many chemists have been inter- nized that jellies can be produced without heat and we have ested in pectin from various standpoints. A study of the household recipes for ‘‘sun jelly” or “cold jelly.” Currants splendid work of FellenbergI5 with its accompanying bib- are the outstanding possibility for making cold-process jelly, liography brings one about up to the date of that publication as they normally contain plenty of pectin and acid without in his knowledge of pectin, though Ehrlich14 attacks the ques- concentration of the juice, but other fruit juices can be used tion of the chemical constitution of pectin in a fundamental when the fruit is in just the right condition. It was but natural that after the role of pectin in jellyway and makes a distinct contribution to that subject. making was- recognized a-tMany others have worked tempts should be made to or are working on pectin, isolate this substance and a n d t h e literature is inA brief review of patent and other literature bearing by its use secure better concreasing in volume and in on the manufacture of pectin prefaces a discussion of trol of the jelly-makingprocvalue. the principles utilized in the recovery of this article. ess and eliminate the uncerRaw materials are apple citrus and beet refuse pulp or Present Status of Pectin tainty or f a i l u r e d u e t o Work carrots. variation in different kinds The production of pectin is followed through the sevThe lack of standard of fruits or in the condieral stages in its development, from the use of apple nomenclature is recognized tion of fruit of the same pectin stock to assist in jelling the juice of other fruits to by everyone who studies variety. the production of a dry pure pectin from citrus fruits pectin literature, and alJelly Stock by the application of principles of colloid chemistry. though there is now some Probably the first use of t e n d e n c y toward better added pectin was by the agreement in this matter there is urgent need for absolute uniformity. Other great housewife, when she learned that by mixing juice from cooked needs are for a knowledge of the actual chemical identity of apples with the juice of berries she could make a firm jelly which pectin and a rapid accurate method for its determination. could not be produced from the berry juice alone. From There is disagreement as to the composit’ion of the various this the practice grew into the production of “stock,” which pectin bodies, and TutinZ8J9J0denies the existence of proto- was a pectin solution obtained by boiling apples, apple pomace pectin as the precursor of pectin as proposed by T s c h i r s ~ h , ~or~ apple skins, cores, and trimmings, and straining off the liquid. This mas the simplest method of extracting pectin. S u ~ h a r i p a and , ~ ~ others. Boiling converted protopectin into pectin and the latter being Function of Pectin in Jelly soluble in the dilute solution of malic acid, there was obtained Regardless of these differences of opinion as to the exact a solution of pectin that could be used to enrich juices deficient nature of pectin, or indeed as to whether pectin is a chemical in this substance. When adopted by the jelly manufacturers this practice was individual or a family of substances, the name is generally accepted as meaning that thing occurring in fruit and other subject to gross abuse, and thousands of tons of jellies paraded parts of plants by virtue of which, in combinations with proper under attractive labels indicating the presence of fruits which amounts of sugar, acid, and water, fruit jellies acquire and were either entirely absent or present in such small proportions maintain their consistency as jelly. The term “fruit jellies” that they gave no distinctive character to the product. This is used in a general sense to cover also jams or any other fruit abuse was the initiator of its own correction. Thanks to the preparations that normally have the consistency of jelly efforts a t proper legislation and its enforcement, bad conditions are being corrected and the better element of the jellywhether they contain fruit pulp or only clear juice. making business is actively interested in the proper use of 1 Presented as a part of the Symposium on Pectin before the joint pectin and in legal restrictions that will eliminate the abuses meeting of the Divisions of Agricultural and Food Chemistry and of Bioassociated with it. logical Chemistry with the Division of Sugar chemistry at the 70th Meeting Attempts a t the recovery of pectin and studies of its use in of the American Chemical Society, Los Angeles, Calif., August 3 to 8, 1925. jelly-making have not been confined to commercial firms, but * Numbers refer t o bibliography at the end of article.
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