present' knowledge of these macromolecules but may also shed some light upon their mode of initiation and termination.
LITERATURE CITED
(1) Anet, F. A. L., Can. J . Chem. 39,
2262 (1961). ( 2 ) Cavanaugh, J. R., Dailey, B. p.9
J . Chem. Phys. 34, 1099 (1961). (3) Edwards, R.3 Chamberlain, s.F., J . Polymer Sci. A l , 2299 (1963). (4) Tiers, G. T'. D., J . Phys. Chem. 62, l l j l (1958). ( 5 ) Williams, R. B., Chamberlain, S. F.,
w.
ACKNOWLEDGMENT
thank R' K' Saunders> T' J ' Denson, and The0 Hines for running the S h I R spectra.
6th World Pet. Congress, Frankfurt, West Germany, June 19-26, 1963, Section T', Paper 17.
RECEIVEDfor revielv June 10, 1964. Accepted July 22, 1964. Presented in part at the Fourth Omnibus Conferencz on the Experimental Aspects of N M R at Pittsburgh, XIarch 1, 1963, and at Sixth World Petroleum Congress, Frankfurt, West Germany, June 19-26, 1963.
N e w Approach to Separation of Trivalent Actinide Elements from Lanthanide Elements Selective Liquid-Liquid Extraction with Tricaprylmethylammonium Thiocyanate FLETCHER L. MOORE Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b Preferential liquid-liquid extraction of the anionic thiocyanate complexes of the trivalent actinide elements with tricaprylmethylammonium thiocyanate dissolved in xylene or other solvents affords a new, improved method for their separation from the lanthanide elements. The order of decreasing extractability i s californium berkelium americium, curium ytterbium thulium europium promethium yttrium > cerium lanthanum. Various dilute acids enhance the separation factors markedly. Among the advantages of this method are the high single stage separation factors possible and the elimination of neutron hazard and corrosion problems associated with lithium chloride-hydrochloric acid systems. Several useful analytical and process applications of the method are discussed.
> > >
>
> >> > >
was published ( 5 ) . The method is based on the preferential extraction of the trivalent actinide elements from dilute hydrochloric acid-concentrated lithium chloride solution with triisooctylamine dissolved in xylene or other diluents. Process studies along the same theme have also been reported (1). This method is currently employed successfully by workers in the field. More recently, interest has centered on an intensive search for a chloride-free liquid-liquid extraction system for this difficult separation. Among the important advantages of such a system would be the elimination of viscous,
highly corrosive solutions of lithibm chloride-hydrochloric acid. I n recent studies ( 1 4 , extractions by di(2-ethylhexy1)phosphoric acid or 2-ethylhexylphenylphosphoricacid from simple carboxylic acids and aminopolyacetic acids appear to be potentially useful for the purification of americium and curium but probably not for the heavier actinides. T o date, the only chloride-free system for the trivalent actinide-lanthanide group separation is that of the solid anion exchangethiocyanate method (!?> 3, 6 , 10. 12). Selective liquid-liquid extraction of the anionic thiocyanate complexes of the
OO 'J
F
among the problems which confront the chemist in the transuranium field is the separation of trivalent actinide elements from the lanthanide fiqsion products. This separation has traditionally involved the use of ion exchange techniques (6, 10) because of the close similarity of the two groups. Workers have long sought simpler separation methods because of the disadvantages common to the solid ion exchange resins. Liquid-liquid extraction is often a preferred method of separation because of its simplicity, speed, and applicability to both tracer and macro amounts of ions. In 1961 the first solvent extraction separation of the trivalent actinide elements from the lanthanide elements OREMOST
21 58
ANALYTICAL CHEMISTRY
A M M O N I U M THIOCYANATE CONCENTRATION, M
Figure 1. Extraction of americium-24 I and europium-1 52-4 tracers from 0.2N sulfuric acid solution with 30% Aliquot 336-S-SCN-xylene
actinide group offers considerable potential. Several chemists (3, 6, 7 , 12) have speculated on this attractive possibility utilizing high molecular weight secondary and tertiary amines. However, no such successful separation has been previously developed. This paper reports the recent successful development of such a system. EXPERIMENTAL
extractions. Tertiary amines, e.g., triisooctylamine, tricaprylamine-were useful under certain conditions but were not investigated in detail because material balances were often poor. The quaternary amine, Aliquat 336-S (tricaprylmethylammonium chloride), was superior to all other extractants tested and was studied in detail. It is cheap, readily available, and possesses the desirable properties of high organic solubility and low aqueous solubility. It may be dissolved in a suitable diluent and used without conversion to the thiocyanate salt. I n this case, because thiocyanate extracts, considerably higher aqueous concentrations of thiocyanate ion are necessary to give extractions equivalent to those possible with the Aliquat 336-S-SCN. For most purposes, it is desirable to use the amine-thiocyanate salt as the extractant. The mechanism of the extraction of americium is of the following type
Apparatus. NaI(T1) well-type gamma scintillation counter, 13/a X 2 inches. Reagents. Aliquat 336-S (tricaprylmethylammonium chloride) is available from General Mills, Inc., Kankakee, Ill. I n t h e formula RICHINCl, R is a mixture of CS and Ci0 carbon chains with the Cs predominating. The reagent grade product contains a minimum assay in the active ingredient of 95 to 98% with a n average mclecular weight of 442. Several different batches of the reagent gave identical results within experimental error. 3070 (iv./v.) ALIQUAT336-S-XY LENE. Dissolve 300 grams of Aliquat 336-S in 1 s(SCN)- e Amf3 liter of reagent grade xylene. Store in a Am(SCN).3-z (1) glass bottle. 3070 ~ L I Q U A T 336-S-SCN-XYLENE. ~[RICHINSCN](,) T o convert the Aliquat 336-5 into the Am(SCN) T3--2 thiocyanate salt, equilibrate the 30% Aliquat 336-S-xylene for 2 minutes with [ ( R I C H ~ N ) , A ~ ( S C ~ J ) , I ,t ,, an equal volume portion of 6M sodium thiocyanate solution in a suitable separatory funnel. After the phases where RICHINSCN = tricaprylmethylhave disengaged, discard the aqueous ammonium thiocyanate (Aliquat 336phase and repeat the treatment a second S-SCN) and the subscript o refers to time with fresh sodium thiocyanate the organic phase. solution. Centrifuge the treated organic phase in 50-ml. centrifuge tubes for 5 The formation of aqueous anionic minutes and carefully decant into a glass thiocyanate species of americium (Equareagent bottle. For less concentrated tion l ) is followed by the extraction solutions of the reagent, dilute and mix of the complex (Equation 2). The well with the appropriate volume of quaternary ammonium compound and xylene. 30Y0 ~ L I Q U A T ~ ~ ~ - S - S C N - X Y L E N Eits salt with the americium thiocyanate complex are essentially insoluble in ( H 9 S O 4 - T ~ ~ . 4 ~ Equilibrate ~~). the aqueous solutions but exhibit high 3070 .\liquat 336-S-SCN-xylene once for solubility in most organic solvents 2 minutes with a n equal volume portion of 11%’ sulfuric acid solution. CentriDepending on conditions, the extracfuge as described above. tion of americium varied as the first, A11 other chemicals were reagent second, or third power of the aqueous grade and used without further purithiocyanate concentration-suggesting fication. Either sodium, potassium, the extracting species, Am(SCN)a-, or ammonium thiocyanate may be used. Am(SCN),-*, and Am(SCN)6-3, reAmmonium thioryanate is recomspectively. For instance, for 0.2N mended in cases where a minimum sulfuric acid solutions containing 0.10solids content is desirable, as in alpha 0.24J1 ammonium thiocyanate, the exparticle counting. Traces of iron in the reagents may give the characteristic traction varied directly as the first red color occasionally, but no interpower of the thiocyanate concentraference occurs. tion; at aqueous thiocyanate concentrations in the approximate range 1-2.451, RESULTS AND DISCUSSION the extraction varied directly as the Exploratory experiments revealed third power of the thiocyanate conthat xylene solutions of various high centration. Under the conditions used molecular weight secondary and tertiary for many of the described separations amines and quaternary ammonium (0.6M ammonium thiocyanate-0.2N salts readily extracted the anionic sulfuric acid), the extraction of amerthiocyanate complexes of americium icium varied directly as the square and europium from aqueous solutions; of the amine concentration. The free in some rases, interesting separation acid concentration in the system critfactors were achieved. I n general, ically controls the nature of the species secondary amines were less effective in solution. and primary amines gave negligible The marked difference in extract-
Table 1. Extraction of Americium-241 Tracer with 30% Aliquat 336-S-SCNXylene as a Function of Time
Americium tracer extracted, 7‘
Time, minutes 0.25
88.8 88.3 87.8 89.6
0.5 1 2 3
86.4
Table II. Extraction of Americium-241 and Europium-1 5 2 - 4 with 3Oy0 Aliquat 336-S-SCN-Xylene as a Function of Phase Volume Ratio
Organic/ aqueous volume 0.25
Tracer extracted, 7c Eu-152-4
Am-241
33.3
99.9 55.3 30 7 99 9 91 4 7 6 51 3 1 1 20.8 99.0
Table V. Stripping of Americium-241 Tracer from 3070 Aliquat 336-S-SCNXylene Solution
Strippant 1 S HzS04 6 S HzS04 1 S HC1 6 S HCl Ilistilled water Ilistilled water, double volume
2160
Am-241 tracer stripped, % >99 9 >99 9 >99 9 >99 9 67 2 85 4
ANALYTICAL CHEMISTRY
pH < 2 had not been studied previously by workers using the solid ion exchangers. Preferential ext,raction of the actinidethiocyanate complexes is possible in the absence of other acids under certain conditions. Because separation factors are poorer a n d hydrolysis problenis become more prominent in such cases, the addition of sulfuric acid is recommended. Many other acids can be used under equivalent conditions to enhance this separation. Among these are hydrochloric, nitric, acetic, tartaric, and citric acids. Hydrochloric acid is just as effective as sulfuric acid, but its lower selectivity, and higher corrosive properties will eliminate it for some applications. Nitric acid has the disadvantage of slowly oxidizing the thiocyanate ion. However, concentrations of 0.1X nitric acid or less were satisfactory for the separation with no mechanical problems. Experiments in which the aqueous phase acidity was adjusted to 0.06N nitric acid-0.2N sulfuric acid gave separations comparable to those obtained for 0.21V sulfuric acid. Thus, one may dilute the nitric acid as much as is practical and adjust to the desired acidity with sulfuric acid. Interestingly, a single extraction with an equal volunie portion of 30y0 Aliquat 336-S-SCS-xylene removed 76% americium and only *4% europium from an aqueous solution containing 0.06,V nitric acid and no ammonium thiocyanate. A4cetic, tartaric, and citric acids (probably most organic acids) show a similar effect to the mineral acids, although to a lesser degree. This is useful where the group separation is required in ion exchange eluant solutions containing organic complexing agents. The americium-241 tracer may be stripped readily from t,he organic phase with aqueous solutions of sulfuric acid or hydrochloric acid (Table V). The procedure used was to mix the organic phase containing 2.3 X lo5 alpha c.p.m. per ml. of americium-241 tracer for 2 minutes with equal volume portions of various strippants. Several experiments using macro amounts of lanthanum indicated no deleterious carrier effect at concentrat,ions of 2 mg. per ml. Higher concentrations were not investigated, but it is anticipated that considerably larger amounts of lanthanide elements could be tolerated. Diethylbenzene was as efficient a diluent as xylene for the bliquat 336S-SCS. Diethylbenzene is a popular process diluent because of its radiation resistance. Doubtless, many other diluents may be employed, although the use of several per cent of modifierse.g., tridecanol, butyl cellosol\~e-prob-
ably will be necessary with kerosine and some aliphatic compounds. The described liquid-liquid extraction system ~vill probably exhibit higher radiation resistance than the solid anion exchanger-thiocyanate systems. The latter require slow flow rates because of the slow equilibrium between the lanthanide elements and thiocyanate ( 4 ) . This promotes decomposition of thiocyanate to produce free sulfur and gas bubble formation causing mechanical problems. These difficulties will be minimized in the liquid-liquid extraction method because it exhibits rapid equilibrium and operates at much lower thiocyanate concentrations; furthermore, the alpha radiation density may be diluted as desired in the solvent extraction method. Further studies were done with some typical trivalent members of the lanthanide and actinide series. Aqueous solutions containing 06.1.1' ammonium thiocyanate and various actinide and lanthanide element tracers were extracted for 2 minutes a t room temperature with equal volume portions of 30y0 -4liquat 336-S-SCN-xylene, After centrifugation each phase was analyzed. S o attempt was made to increase the separation factor by obvious scrubbing proc,edures. Aqueous sulfuric acid concentrations of 0.LV and 0 . 2 5 were used to show the marked acid effect. Typical data shown in Table IV indicate that high separation factors for trivalent actinide and lanthanide elements are possible, thereby providing a practical method for the group separation. The order of decreasing extractability found is californium > berkelium > americium, curium >> ytterbium > thulium > europium > promethium > yttrium > cerium > lanthanum. The actinide elements-thorium, protactinium, uranium, neptunium, and plutonium-were not tested inasmuch as their separation from the lanthanide elements is relatively simple because of their higher oxidation states. I t can be predicted ( d ) , however, that the behavior of the trivalent, states of these actinides would be closely similar to that of aniericium(II1) and curium (111). Actinide elements above californium were not available for study, but their trivalent oxidation states would be predicted to behave similarly to californium(II1). Several combinations of variables may be used for the group separation dictated by the objective, either quantitative recovery or a certain degree of decontamination of the trivalent actinide group. The conditions described in Table IV are not necessarily the best but simply indicate the potential of the new method. For instance, in niultistage work the use of lower concentrations of ammonium thiocyanate
and higher concentrations of free acid mag be desirable. Also, more dilute solutions of Aliquat 336-S-SCN give somewhat better mechanical behavior. T'pon applying the extraction procedure described for Table IV in multiextraction experiments, it was observed that the extraction coefficient of the lanthanide elements increased during the second and third extractions with fresh portions of solvent, thereby reducing the separation factor. Further studies showed this effect to be caused by the removal of some of the free acid from the aqueous phase by the extractant. Pretreatment of the Aliquat 336-8-SCN-xylene solution for 2 minutes with an equal volume portion of 0.2.V or 1 . O S sulfuric acid (or equivalent hydrochloric acid) solution alleviated this problem. A l . O X sulfuric acid solution is recommended for the pretreatment. The method described in this paper has been tested in several demonstrations. Separation of Americium from Promethium or Europium. Because of their almost, identical ionic radii, t h e chemical behavior of trivalent americium and promethium in most aqueous solutions is similar. Thus, in t h e purification of the individual lanthanide radioisotopes, americium elutes with promethium from cation exchange resins with solutions of ammonium citrate, ammonium lactate, ammonium tartrate, ammonium glycolate, and ammonium a-hydroxyisobutyrate. X recent development (9) describes the use of diethylenetriaminepentaacetic acid as an eluant to shift the elution of americium to the europium fraction. To demonstrate the separation of americium from promethium or europium, aqueous solutions containing americium-241 (7 X lo4 alpha c.p.m.) and promethium-148 (1 x lo4 gamma c.p.m.) or europium 152-4 (4.6 X lo4 gamma c.p.m.) were adjusted to a concentration of 0.1N sulfuric acid-0.6M ammonium thiocyanate. A 2-minute extraction at room temperature was performed using an equal volume portion of 20% Aliquat 336-S-SCN-xylene (H2S04-treatedj . The extraction was repeated with a fresh portion of solvent. Extractions averaged 94.8% for americium-241, 4.7% for promethium-148, and 5.8% for europium-152-4. Separation of Trivalent Actinide Elements from Lanthanide Fission Product Mixture. A solution (1 X 10' alpha c.p.m. per mi.) containing americium-241, curium-244, and californium-252, and a lanthanide fission product mixture (5 X lo4 gamma c.p.m. per ml.) containing cerium-144, promethium-148, europium-152-4, and yttrium-91 was adjusted to a concentration of O . 1 N sulfuric acid-O.6M
ammonium thiocyanate. A 2-minute extraction at room temperature was performed with an equal volume portion of 20% Aliquat 336-S-SCN-xylene (H2S04-treated). The extraction was repeated twice with fresh portions of the solvent. Similar experiments using 30% Aliquat 336-S-SCN-xylene (H804treated) were performed. The results shown in Table VI indicate that excellent separations of the trivalent actinide group from the lanthanide group may be achieved in a few stages. No scrubbing steps were used in these demonstrations. APPLICATIONS
This new method is useful for a variety of applications. Rapid Separations for Analysis. Preliminary separation of t h e lanthanide elements is often necessary prior to alpha energy studies of the actinide elements because of t h e high levels of beta, gamma radioactivity present. Moreover, some conventional counters (as Frisch Grid chamber) exhibit low beta tolerance. T h e beta-, gamma-emitting lanthanide elements may be easily removed from the actinide elements by the method described. Because quantitative recovery is often unnecessary, one may apply appropriate extraction conditions for recovery of substantial yields of high purity actinide elements. For instance, one extraction effects essentially a quantitative separation of californium from lanthanum, a popular carrier for actinide elements. General Purification Work. By proper choice of conditions, t h e radiochemist can effect quantitative group separations of t h e trivalent actinidelanthanide elements. T h e described separation of americium from promethium a n d europium should be valuable in t h e industrial purification of these radioisotopes. The laboratory scale experiments reported here can be applied even more efficiently on a large scale, For the separations technologist the method offers such desirable features as speed, ready adaptability to remote control, and continuous countercurrent processing at room temperature combined with the relative radiation resistance of the high molecular weight amines. I n addition to these features, some of the significant advantages of the amine-thiocyanate system over previous methods for this group separation are as follows: Highest single stage separation factors found to date are effected. [Californium(111) / Lanthanum(II1) ] = 9800 and 5000 a t 0.2N and 0 . l N sulfuric acid concentrations, respec[ Berkelium(III)/Cerium tively. ( I I I ) ] = 1700 and 1400 a t 0.2N and 0.1N sulfuric acid concentrations, respectively.
Table VI. Separation of Trivalent Actinide Elements from Lanthanide Fission Product Mixtures
Tracer, extracted, No. of
Extractant
-
70
extractions
Actinides
Lanthanides
2
936
3 1
3
99 3
-5.2
2
97.9
5.1
207' Aliquat
336-S-SCNxylene ( HzSOItreated) 20% Aliquat 336-S-SCNxylene (HPSOItreated) 307' Aliquat 336-S-SCNxylene (HZSOI-
treated)
Higher solubilities of lanthanide, actinide, and other elements are possible than in the concent'rated lithium chloride system. The amine-thiocyanate system is considerably more versatile in free acid requirements. For instance, higher concentrations of free acid may be used than in the lithium chloride system. Moreover, many acids other than hydrochloric acid function efficiently in the aminethiocyanat'e system. Equilibrium is reached rapidly, thereby eliminating kinetic prot.lems. The amine-thiocyanate system is relatively noncorrosive as contrasted to the highly corrosive lithium chloride-hydrochloric acid system. For the processor, this eliminates the need for expensive corrosion-resistant metals such as tantalum-thereby providing a large cost reduction. Viscosity problems encountered with sirupy solutions of concentrated lithium chloride are eliminated. More dilute aqueous concentrations of t,hiocyanate ion may be employed in the amine-thiocyanate system than in the solid ion exchange resin methods. The latter use thiocyanate ion concentrations in the range, 4-8.11 (4,8, 11, 13) for practical separations. I n the amine-thiocyanate system, the trivalent actinide elements are extracted away from the highly radioactive lanthanide elements. This is more desirable than extraction of the lanthanide elements because relatively large amounts of these (as larthanumj are often present, necessitating large volumes of extractant. The amine-thiocyanate system eliminates the neutron hazard which exists in systems using concentrated lithium chloride in the presence of large amounts of alpha emitters. A liquid-liquid extraction system provides a simple method of diluting the radiation density, a desirable feature impractical with solid ion exchange resins ( 4 ) . VOL. 36, NO. 11, OCTOBER 1964
0
2161
LITERATURE CITED
( 1 ) Baybarz, R. D., Weaver, B., Leuze, R. E., N d . Sci. Eng. 17,457 (1963). (2) Diamond, R. M., Street, K., Jr.. Seaborg, G. T., U . S. At. Energy Comm’, Declassified Rezk UCRL-1434 (Rev.) (1951). (3) Faure, A., Weaver, B., Ibid., ORNLTM-107.4411961). (4) Keenai, T: K., 3. Inorg. Nucl. Chem. 20, 185 (1961). (5) Moore, F. L., ANAL. CHEM.33, 748 (1961). ( 6 ) .Moore, F. L., “Liquid-Liquid Extrac~
tion with High-Molecular-Weight Amines,” NAS-NS-3101 (1960); avail-
able from the Office of Technical Services, Dept. of Commerce, Washington 25, D. C. ( 7 ) Moore, F. L., unpublished work, Oak Ridge National Laboratory, Notebook NO. 1428 (1951-1952). (8) Naito, K., U. S. At. Energy Comm.
Unclassified Rept. UCRL-8748 (1959). ( 9 ) Orr, P. B., Ibid., ORNL-3271 (1962). (10) Penneman, R. A., Keenan, T. K.,
“The Radiochemistry of Americium and Curium,” NAS-NS-3006 (1960); available from the Office of Technical Services, Dept. of Commerce, Washington 25, D. C. ( 1 1 ) Ryan, 5’. A., Pringle, J. W., U . 8.
At. Energy Comm. Unclassified Rept. RFP-130 (1960). (12) Sheppard, J. C., Ibid., HW-51958 114.57) \---.,.
(13) Surls, J. P., Choppin, G. R., J . Inorg. Nucl. Chem. 4, 62 (1957). (14) Weaver, B., “Chemical Differences
between the Lanthanides and Trivalent Actinides,” Proceedings of the Fourth Rare Earth Conference, Phoenix, Arizona (April 22-25, 1964). RECEIVEDfor review June 8, 1964. Accepted August 3, 1964. Research sponsored by the U. S. -4tomic Energy Commission under contract with Union Carbide Corp.
Determination of Specific Heat and Heat of Fusion by Differential Thermal Analysis Study of Theory and Operating Parameters D. J. DAVID Mobay Chemical Co., New Martinsville, W. Va.
b Utilization of differential thermal analysis under nearly equilibrium conditions permits the determination of heat of fusion and specific heat on a variety of inorganic and organic compounds from a single calibration of an easily handled material like tin. Variables such as sample size, heating rate, and sample state were studied for their effect upon the heat of fusion. These variables did not exhibit effects upon the results within the limits of error of the determination. The theory and equations underlying the specific heat determination are discussed and a practical method is presented which is applicable to a wide range of materials. The standard deviation at the 95% confidence level for the heat of fusion and specific heat was found to be 1.5 cal./gram and 0.02 cal./ gram/OC., respectively.
D
IFFERENTIAL
THERMAL
ANALYSIS
has been applied previously to a var:ety of both inorganic and organic materials. These applications were initially concerned with minerals and soils ( 8 ,23), and subsequently with pure inorganic compounds ( 7 , 16, 21). More recently, less well defined organic materials and compounds have been studied. The investigators have reported both qualitative and quantitative results ( I , 2, 6, 11, 17, 22, 30, 31). As a result of the gradual development of a variety of differential thermal analyzers, a re-evaluation of qualitative and quantitative variables has resulted in some duplication of effort ( 2 7 ) .
2162
ANALYTICAL CHEMISTRY
The variation of peak temperature has been reported to be dependent upon sample size, size of the cylindrical holder, and heating rate ( I d , 84, 28). The effects of diluent techniques have been covered in various papers. Particle size and packing were found to be important factors that affected the thermograms obtained (19). I n addition, the formation of complexes with the inert diluent has also been reported
(4, 18).
However, with the development of more sophisticated and sensitive instrumentation, the effect of sample size, diluent, size of sample holder, heating rate, and difference in heat capacities between reference and sample, and other parameters can be better evaluated. Base line deviation, especially a t the beginning of a run, is a common occurrence in differential thermal analysis. This is due to an imbalance in heat capacities between the sample and refer nce thermocouples and is affected by symmetry, sample loading, inert loading, and packing ( 3 ) . Many of the detrimental and nonuniform parameters that accompany the great variety of techniques common to each specific analyzer, may be turned to advantage when the proper technique is employed as in the present application. The aspects of differential scanning calorimetry (DSC) pnd applications to quantitative measurements of tranyition energies have been reported recently by Watson, et al. and O’Neill (20>29). DSC measures the transition energy
directly (29) while conventional DTA measures AT v s . sample temperature. Thus, DT-4 must be calibrated before it can be utilized for quantitative transition energy measurements. The present paper will show that when D T A is carried out under nearly equilibrium conditions, a single calibration can be performed which is applicable to the determination of the specific heat and heat of fusion of both organic and inorganic compounds. THEORY
The major factors affecting base line deviation (equilibrium conditions) are mismatched heat capacities, improper heat transfer, symmetry, packing, particle size (sample and diluent), dilution effects, inertness of diluent, and sample concentration. When a sensitive system is employed in which the sample size is small (1 to 10 rng.), the sample does not have to be diluted, and the system contains fixed thermocouples allowing reproducible results; the disadvantage of base line deviation can be an asset by allowing the determination of the specific heat of the sample. hssuming the above conditions exist, the deviation in base line would be greater for those materials w‘th a high specific heat value. To obtain a mathematical expression for C,, we must consider two factors: the effects of the system upon the differential thermocouple; and the effectsof the system plus sample upon the differential thermocouple.
