Production of Low Temperatures A Simplified and Inexpensive Laboratory Procedure IIELEU L. WIKOFF, B E V J i \ I I K R. COHE?,
4hD
JIOKTON I. GROSS\I
S
EVERAL of the more recent advances in biological
\>, The Ohio S t a t e L ni\ersit>, Colurnl,us, Ohio
is not availalile to the average chemist. To be of greatest value, such a scheme should provide an inexpensive method for obtaining lon- temperatures, preferably on an ordinary lalioratory table. Temperatures should remain fairly constant for appreciable time intervals and neither health hazards nor fire hazards should be introduced in the protluction of the cold. Brown and Stoner ( I ) clesrihe a method by wliicli, by acltling a sufficient quantity of solid carhon dioxide t o alcohol, they lvere able to reach temperahres ranging from - 50" to -60" C. in 20 to 30 minutes and as lo^ as -75" C.in a little longer time. These investigators also had access to a cold room with a temperature range bet's-een -20" antl -25" C., nliere they carried out many of their laboratory procedures. Using their procedure, a l o ~ vtemperature may be produceil at' a relatively low cost. However, the use of a volatile solvent such as ethyl alcohol must be considered as a hazard t'o health and a distinct fire hazard. I n order to overcome these ohjections and to secure a greater consistency in the teinperature niairitained, tlie follou-ing investigation was undertaken.
chemistry depend upon the use of low temperatures; temperatures ranging froin -20" t'o -75" C. are frequently required. With proper insulation antl a good compressor system, temperatures ranging between -35' and -40" C. may be obtained by the use of liquid ammonia, and if liquid carhon dioxide is substituted for ammonia in tlie cooling system, temperatures between -51" and -56" C.are possible. Still greater compression by means of a booster is needed to produce a temperature of approximately -84.5' C.used for making "dry ice" froin carbon dioxide. However, the cost of installing the apparatus required makes these methods of cooling practically out of the question for the small chemical laboratory. Liquid air enables one to obtain t'einperatureu of about - 140" C., but costly apparatus is needed to produce the liquid air, while very special care is necessary in handling the chilly fluid after it has been manufactured. Consequently liquid air plays practically no part in the production of l o x temperatures for general biological work. Small "cold rooms", operat'etl a t a minimum temperatiire of -20" to -25" C. antl designed primarily for storage purposes, are sometimes used in biological work but, though ideal for cold-storage purposes, are scarcely suitable places in which to work. Individuals n h o must enter and leave a cold room a t frequent' intervals are apt to become careless about proper warnitli in dress; one case of pneumonia contracted during a hot, suiiimer season by a research worker using such a cold room has come t'o the authors' attention. On the other liaiid, if workers are properly dressed to protect themselves ngaiiist cold, their ability to manipulate delicate chemical apparatus is likely to be greatly harriperecl 1)sgloTes ant1 extra clot'liing. Holyever, biological cheniists in general are not confronted by these problems because t,he cost of inst,allatioii greatly limits the number of such rooms in operation. There is a definite need for a system in which low tenipci,atures can be obtained without tlie use of a cold romn, wliich
Procedure Tlierriios bi.anc1 vacuum-insulated containers of Pyrex t)i,and d in all the loxv-temperature Jvork. The 1000-cr. ( S o . 8645, t,lie American Thermos Ihttle (:ompany) with full-diameter 6.88-cm. (2.73-inch) openings and 39.7-em. (11.875-inch) inside depth were of such size thttt teat tubes or small bottles could be lo~veredinto the cold mixture. A larger container of 4300-cc. capacitj- (No. 8642) ivith a fulldiameter 16.95-cni. (6.78-inch) opening and 27.19-cni. (10.875inch) inside depth \\-auld accommodate an Erlenmeyer flask having :I c:ipacity of 1 liter. . 4 container having a capacity of ~ I I proximately 41,371 cc., a full-diameter opening of 30 cni. ( I 1.75 iiiclie-), aiid inside depth of 71.6 cni. (28.23 inches), is also nianufactured ant1 will accommodate riiurli 1:wger vesels, hut ~ v a . iiot uqed b y t h c authors. In ulder better to protect, insulate. :tnd identify cont:tiiiers, a 1,ectnngular copper jacket \vas provided to acconimotfatc four flasks of tlir smaller rapacitJ-. This box i v a s 68.75 e m . (27.5 inrheb) long, 2 2 . 5 cni. (9 incliey) \vide, and 37.5 cm. (15 inclie.;) high and \ v a ~di\rided into four q u a l conipartnicuti b!, cro'is ~
Produota 197.2 187.:;
E t h y l e n e glycol HO.CH?.VH:OH Prop>-lpne XI> col CI~~.CHOH.CIIIOII Diethylene glycol HO.CH~CH?.O.CH~.CH..OtI Dipropylene glycol CHa.CHOH.CH,)rO H O . C H : . C H z . O . C € ~ ! . C H n O . C ~ ~ ! .tI~ H ~ ( ~ Triethylene glsool ~CH~~CHI.CH?.O.CI~~,CH~~~O Dimethoxvtetraethvlene glycol J I e t h y l Cellosolve Cellosolre Diethyl Cellosolve nut,.l Cellosolve Phenyl Cellosolve Benzyl Cellosolve N e t h y l Cellosolre acetate Celloauive acetate hIethyS Carbitol Carbitol Iiieth) I Cai;bitol Hut>-I CarbiroS Carbitol acetate But>-ICarbitol acetate Diacetone alcohol a IIaterials used a? purchased f r o m ('arbide and Carbon ( ~ l l e w i r a l >( ' u r y b Values t a k e n f r o m f 2 ) . c Supercools, temperature of crystals - 17'.
244,: 229,2 288.0 273.8
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- 37 - ,58 -x 1
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12 0.97 0 ,0:; 0 ,0 2 3.i3 1.09 0 ,2 0.1 0.48 0.1 0.1
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92
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- 77 +l:'
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-7ii - 65 -54 -71; -67
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Gla~slihe Thick Glasslike thick
.ANALYTICAL EDITIOS
FEBRUARY 13, 1940
93
part,itions. Each bottle was further protected by a covering of loose cotton between it and the copper wall. Numbers on the outer side of the copper jacket served to identify the flasks, and a long copper lid with handles on either end protected the contents of the containers. An individual cylindrical copper jacket, 37.5 cni. (15 inches) high and 23.75 cm. (9.5 inches) in diameter, accommodated the 4300-cc. container well wrapped with cotton. A copper lid with a handle was also provided for this jacket. Low temperatures ivere obtained in the 1000-cc. containers by slowly adding 115 t o 170 grams (4 to 6 ounces) of dry ice (in small pieces) to about 500 cc. of the nonvolatile liquid to be tested. About 1 liter of fluid was used in t,he large container with a corresponding increase in dry ice. The slow addition of the dry ice prevented the liquid from being spattered out of the container by too rapid an evolution of carbon dioxide. The temperature was generally lowered appreciably within a few minutes and further additions of dry ice could then be made with little danger of splattering.
Cellosolves studied, but the viscosity of the liquid increases so greatly as the temperature decrex-es that benzyl Cellosolve is of no value in a cooling bath. The introduction of a n acetate radical reduces the vapor pressure of the Cellosolves to some extent. However, methyl Cellosolve acetate is apparently sufficiently toxic to warrant a warning label on the container and therefore is not recommended for cooling mixtures, despite the fact that it remains water-thin with dry ice at a temperature of -76" C. Cellosolve acetate, nitli a vapor pre5sur.e of only 1.09, also remains water-thin a t -76" C.
Since the vapor pressures of the glycols are much lower than those of the corresponding monohydric alcohols, i t was decided to investigat'e the possibilities of the former series for the production of cold by the addition of solid carbon dioxide. All the glycols available in a commercial grade, as \vel1 as the related compounds known by the trade names of Cellosolves and Carbitols, were subjected to the procedure outlined above. Unless the material being tested crystallized, more dry ice was added from time to time until the presence of a large excess of dry ice caused no further reduction in temperature after standing several hours. Table I lists t'he compounds used together with t'heir behavior when treated with solid carbon dioxide.
- 1 .?I =-1 Ethylene glycol Dimethoxytetraethylene glycol -31 i l - 5% *l Diethyl Carbitol 67 j.2 Carbitol acetate Cellosolve Cellosolve acetate - 73 -7 7 u Diacetone alcohol i depending on physical conditions, includButyl Cellosolve , ing length of standing with excess d r y ice
Discussion -\lost' of the glycols become very thick and viscous as they cool after the addition of dry ice and their consistencies a t the lowest temperatures recorded resemble that of partially molten glass. If crystallization ultimately does take place in some of these solutions, tlie fluids hare become supercooled to such an extent that the entire mixture solidifies. Consequently diethylene glycol, trietliylene glycol, propylene glycol, and dipropylene glycol when treated with solid carbon dioxide are worthless as fluids for cooling baths. Ethylene glycol, n-hicli cryst,allizes from the carbon dioxide solut,ion a t -Eo, neither thickens nor supercools. If the dry ice is added carefully so as to avoid the presence of a large excess after reaching a temperature of -E", most of the ethylene glycol can be kept in solut'ion and a constant' teinperatrire of -15" * 1" C. maintained for a t least 4 hours without even closing the container. Dimethoxytetraethylene glycol begins to crystallize from a solution saturated vitli carbon dioxide a t -29" C . 13y carefully avoiding a large excess of thy ice, the authors were able to maintain a temperature of -31" * 1 " C. for 6 hours without adding more ice or causing more than a small amount of crystallization at a room temperature of 30". The Cellosolve series produces much loiver temperatures with dry ice. Phenyl Cellosolve, crystallizing a t +12" C., is the only striking exception to this general statement. Methyl, diethyl, and butyl Cellosolve, as \vel1 as the original Cellosol\.e, all reach low temperatures ranging from -76" to -77" C. on standing. The conyistency of tlie cooled butyl Cellosolve resembles that of glycerol, while the other Cellosolves mentioned remain water-thin a t the lon-est t'eniperatures reached. Hoxvever, because of the appreciable w p o r pressures of the methyl and diethyl Cellosolves, t'hose cornpounds are not recommerided as cooling fluids for use v i t h carbon dioxide. Cellosolve and butyl Cellosolre with vapor pressures of 3 arid 0.97 mm. of mercury, respectively, are suitable for maintaining temperatures of -74" to -77" C. over long periods of t'irne if a sufficient supply of dry ice is added. Benzyl Cellosolve possesses tlie lowest vapor pressure of any of the
'rABLE
11.
F'RODUCING TEMPERITVRES WTII DRYICE
PRODUCTS RECOMMESDED F O R Kame of Product
h I \
Tenlperal ure Produced
=
c.
-
7
a I t is possible t o obtain any desired temperature above -73' for a short Fime interval b y mising a n y of these product:, with the proper amount of dr? ice. However, t h e products listed i n Table I1 will maintain t h e temperature* listed for a t least 4 hours if left nndisturbed.
The Carbitol series seems the safe:t for use in the production of cold with dry ice, since none of tlie compounds investigated possesses a vapor pressure greater than 0.48. 1Iethyl and butyl Carbitol both thicken appreciably as they cool aft'er the addition of dry ice and are not so satisfactory for use in cooling baths as some of the other compounds studied. Furthermore, these two solvents ieool rather slowly beloiv -50" C., although t'eniperatures as lorn as - 7 5 ° C . mayevcntually be registered. After standing overnight, with ail excess of dry ice, methyl Carbitol finally on one occasion crystallized. The temperature of t'lie cryst'alline material was -65' C. Cnrbitol thickens a t -54" C1. and supercools to a t least -65". After &tanclingfor some time a t this temperat8ure, the niat,erial crystallizes ant1 the temperature returns to -54". Diethyl Carbitol crystallizes from the carbon dioxide aolution a t - 54" C. without supercooling or thickening before crystallization. If dry ice is cautiously added to this cornpound so as to avoid a large excess at the crystallization temperature, only a small amount of' the solution mill crystallize aiid the remainder will maintain a temperature of -52" for a t least 4 hours. The Carbitol acetates are useful for producing extreme cold with dry ice. Carbitol acetate, crystallizing at, -73" C. from a water-thin carbon dioxide solut,ion, niay be used for baths of -67" by avoiding too large an excess of dry ice. Butyl Carbitol acetate, thickening to a consistency slightly greater t'han that of glycerol, does not crystallize even in the presence of inuch excess dry ice. Temperatures as low as -72" * 1" C. can be obtained n-itliin 30 minutes and if the butyl Carbitol acetate is allowed to stand in the presence of a large excess of dry ice, a temperature of -76" C . may be registered within a n hour and maintained for more than a day. Diacetone alcohol, although belonging to none of t'he types of compounds already list,ed, \vas rrlso studied. This compound cools very rapidly when dry ice is added, fails to crystallize in the presence of a large excess of dry ice, and remains water-thin a t the lowest temperature observed (-77"). This temperature held for 24 hours if the outer jacket was closed except while observations were being niade. I n actual practice, it has been found more convenient to use a series of loiv-temperature baths, lhan to place the warm object a t once in a container with a bath of an extremely low
INDUSTRIAL ASD ENGINEERING CHEMISTRY
94
temperature. The latter practice will result in the violent evolution of carbon dioxide together with a possible loss of part of the cooling fluid. The same fluid may be used many times by simply adding dry ice whenever a low temperature is desired. If convenient, the solvents may be left in the small Thermos containers which may be closed by corks after the contents have returned to room temperature. When the solvent must be removed from the container, a violent evolution of carbon dioxide together with a possible loss of part of the fluid is likely t o occur if the cold mixture is poured into a bottle or beaker at room temperature.
Conclusions The compounds studied fall into three groups with respect to behavior with dry ice: (1) compounds which crystallize sharply from solutions with carbon dioxide, (2) compounds which thicken and either supercool or fail to crystallize a t all,
VOL. 12, NO. 2
and (3) compounds which neither crystallize nor thicken to any extent. Compounds of the second type are worthless in cooling baths with dry ice. Compounds of the first type will maintain a temperature slightly lower than the initial temperature of crystallization for a few hours if the dry ice is added carefully. Compounds in the third group are merely cooled by the ice and therefore tend to approach -79.5’ C., the melting temperature of solid carbon dioxide. The exact temperature recorded by any member of this group may therefore vary by as much as 4” or 5 O , depending on physical conditions. Table I1 contains final recommendations regarding compounds to be used in producing low temperatures with dry ice.
Literature Cited (1) Brown, J. B., and Stoner, G. G., J . Am. Chem. Soc., 5 9 , 4 (1937). (2) Carbide and Carbon ChemicalsCorp., “Synthetic Organic Chemicals”, table on pp. 6 and 7.
Determination of Small Amounts of Copper and
Manganese In Dyes and Other Organic Materials G. F. PALFREY, R. H. HOBERT, A. F. BENYIYG, AND I. W. DOBRATZ Jackson Laboratory, E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
T
HE demand for so-called copper- and manganese-free
dyes, intermediates, and rubber chemicals for use in rubber and on fabrics to be rubberized necessitated the development, many years ago, of accurate and sensitive analytical methods for determining traces of these elements. I n the authors’ first methods the organic matter was destroyed by dry-ashing, using a procedure similar to the present A. S. T. M. method D377-37. This ashing procedure was unsatisfactory for most dyes. Copper was subsequently determined colorimetrically by the use of potassium ferrocyanide as indicator and manganese by oxidation to permanganate, using potassium periodate as recommended by Willard and Greathouse (4). During the last 10 years methods have been revised several times as the result of investigations of published methods, private communications (S), and suggestions from several analysts who have used the authors’ methods. T h e following methods, which are believed to contain improvements not published previously, are now used officially in this department for the determination of copper and manganese in dyestuffs, rubber chemicals, and rubber. The organic matter is destroyed by wet oxidation with sulfuric and nitric acids followed, when necessary, by hydrogen peroxide. C o p per is then determined colorimetrically using sodium diethyldithiocarbamate as indicator as recommended by Callan and Henderson (1). Manganese is still determined by oxidation to permanganate. As both copper and manganese are generally required on the same sample, the methods have been combined as far as possible.
copper and manganese.’ A 500-cc. Kjeldahl flask and Kjeldah digestion apparatus. PROCEDURE. Accurately weigh approximately 5 grams of the sample and transfer to a 500-cc. Kjeldahl flask. Add carefully 20 cc. of concentrated sulfuric acid and one or two glass beads, place the flask on a digestion rack, and slowly heat it until the mixture boils. Continue to boil gently until complete charring and disintegration of the organic matter have occurred (about 15 to 20 minutes’ boiling is generally required). As sulfuric acid is consumed in the oxidation, add more in 5-cc. portions, when needed, t o maintain the volume at about 20 cc. When charring is com lete, allow t o cool and add carefully, in small portions, 5 cc. orfuming nitric acid. If a strong reaction occurs, stop the addition and swirl the contents of the flask until the reaction subsides, then carefully continue the addition. Heat the mixture with a low flame until the brown fumes have disappeared, boil vigorously for a few minutes, and then cool. Repeat this process until two successive treatments with the nitric acid produce no decrease in color (three 5-cc. portions of nitric acid are generally sufficient). While agitating, dilute the contents of the flask with 100 cc. of distilled water. Boil the solution down to strong fumes of sulfur trioxide and cool. This hydrolyzes the nitrogyl sulfuric acid and drives off oxides of nitrogen. If a yellow color is present in the solution a t this point it is usually indicative of the presence of either iron or undigested organic matter, and the solution should be treated as follows: Carefully add 5 cc. of hydrogen peroxide. Heat the mixture with a low flame to strong fumes of sulfur trioxide, boil vigorously for a few minutes, then cool. Repeat this process until two successive treatments with hydrogen peroxide produce no decrease in color (two or three 5-cc. portions are generally sufficient). While agitating, dilute the contents of the flask with 100 cc. of distilled water. Boil the solution down to strong fumes of sulfur trioxide and then cool. This will remove any excess hydrogen peroxide. I
Destruction of Organic Matter REAGENTS AND APPARATUS.c . P. concentrated sulfuric acid (sp. gr. = 1.842), c . P. fuming nitric acid, and hydrogen peroxide, approximately 30 per cent by volume, and essentially free from
1 “Albone C”, lOO-volume, as manufactured b y the R. & H. Chemicah Division, E. I. d u P o n t de Nemours & Company, he., has been found satisfactory.
