Thermodynamics of extremely diluted solutions

Department of Chemistry, University Federico II of Naples,
via Mezzocannone, 4 - 80134 Naples, Italy

Abstract

The interaction of acids or bases with extremely diluted solutions has been studied calorimetrically at 25°C. Measurements have been performed of the heats of mixing of acid or base solutions, having different concentrations (0-0.05 mol kg-1), with bidistilled water or with the extremely diluted solutions obtained through successive dilutions and succussions. Despite the extreme dilution of the solutions, less than 2*10-5 mol kg-1, an exothermic excess heat of mixing has been systematically found in the totality of cases (beyond 200 experimental measurements) as respect to the heat of mixing with the untreated solvent. Then, the possibility exists that successive dilutions and succussions may alter permanently the physical-chemical properties of the solvent.

Riassunto

L'interazione fra soluzioni di acidi o basi, con soluzioni estremamente diluite, è stata studiata per via microcalorimetrica a 25° C. Sono state effettuate misure di calore di mescolamento fra soluzioni di acidi e/o di basi a diversa concentrazione (0--0.05 moli kg-1) con acqua bidistillata e con soluzioni estremamente diluite, ottenute mediante successive diluizioni e succussioni. Nonostante l'estrema diluizioni delle soluzioni adoperate, inferiori a 2*10-5 moli kg-1, è stato sistematicamente riscontrato, nel 100% dei casi (oltre 200 misure sperimentali di calori di mescolamento), un eccesso esotermico rispetto al calore di mescolamento con il solvente. Dal quadro sperimentale riportato emerge la possibilità che il procedimento di successive diluizioni e succussioni alteri le proprietà chimico-fisiche del solvente in maniera permanente.

1. Introduction

The great interest in the last century, and in particular in the last years, towards the therapeutic effect of remedies used in the homeopathic medicine pulled us to begin a systematic physical-chemical study of the most extrahordinary object of this alternative medicine, namely the extremely diluted solution.

Extremely diluted solutions are prepared usually through the technique proposed by Samuel Hahnemann, which essentially implies the iteration of two processes: dilution and a particular shaking called succussion. For solutes soluble in water, the extremely diluted solution is obtained starting from a 1% in weight or volume solution (f. i. 1 g of solute is added to 99 g of water). After succussion, that solution is 1 centesimal hahnemannian (1CH). The succussion process occurs through the vertical shaking of the solution in mechanical apparatuses. In a single succussion process, one hundred vertical strokes are given to the glass or polypropylene vessel containing the solution. To prepare the 2 centesimal hahnemannian, 1 g of 1CH solution are added to 99 g of water and succussed. The iteration of this procedure leads to extremely diluted solutions. Their dilution degree is such that they can be considered as pure water: then, their physical-chemical properties are to be expected not different from those of pure water.

To the aim of investigating which processes used for the preparation of these extremely diluted solutions are necessary (dilutions, succussions, number of strokes, changes of momentum in every stroke, kind of apparatus, nature of the initially present solute, etc.) and which changes are induced in the physico-chemical behaviour of water, studies have been performed using the microcalorimetric technique. Measurements of heats of dilution of aqueous solutions containing ponderable quantities of solutes having different nature evidenced that some physico-chemical properties of the solvent are different, in contrast with what one should expect. The origin of this different behaviour, which was unequivocally monitored, could depend on a variety of causes, among them the factors cited before: hence, the complexity of the system urged us to look for systems as simple as possible. To be independent of the solute nature, water treated according to the method described to give 1CH, 3CH and 30CH dilutions was chosen as sample system. Then, 3CH and 30CH sodium chloride solutions were also investigated.

Experimental

2.1 Apparatus

Heats of mixing were monitored using a Thermal Activity Monitor (TAM) from Thermometric, equipped with a flow-mixing vessel and a batch titration vessel, able to appreciate 0.1 mW. In the case of the flow-mixing vessel, two peristaltic pumps envoy solutions into the calorimeter through teflon tubes. Flow rates of the liquids are the same and constant in the inlet tubes, so that the solution coming out of the calorimeter has a concentration half the initial one. The mass flow rate employed, constant within 1%, is 3*10-3 g s-1: it is the same for all experiments. Enthalpies of mixing , DHmix, are obtained from the relation:

DHmix (mxiÆmxf) = -(dQ/dt)/PW (1)

where (dQ/dt) is the heat flux (Watt), PW is the total mass flow rate of the solvent (kg s-1) and mxi and mxf are the initial and final molalities, respectively, of the solution. DHmix is expressed in J kg-1 of solvent. The maximum error on the mixing heat is about 10%, while that on the molalities is 5*10-2. Every experimental value is the average of several experimental measurements carried out in the same experimental conditions. The calorimeter has been tested by measuring the dilution enthalpies in water of urea and hexane-1,2-diol. The evaluated enthalpic interaction coefficients (hxx = -331± 3 for urea and hxx = 2999±46 J kg mol-2 for hexane-1,2-diol) are in a very good agreement with those reported in the literature (-350± 13 and 2955±46 J kg mol-2 for urea [1] and the diol [2], respectively).

2.2 Materials

Solutes were Carlo Erba or Baker or Sigma products: they were of the highest purity commercially available. Solutions employed, treated according to the described method, were supplied by Sifra O. (Florence, Italy): they were prepared using only bidistilled water supplied by Carlo Erba. Solutions of the various solutes (NaOH, HCl, etc.) were prepared by weight using doubly distilled water. NaOH solutions were protected from the contact with atmospheric carbon dioxide by means of suitable traps.

2.3 Methods

Every calorimetric measurement is carried out comparing the behaviour of pure water, when mixed with the test solution, and that of the extremely diluted solution interacting with the same solution, in the same experimental conditions. Both the extremely diluted solution and the bidistilled water used as solvent are stored in vessels of dark glass for the same time. In Fig.1, a typical power-time plot is reported. Line A represents the steady-state reached when solvent water is sent into the calorimeter in both the inlet tubes (baseline). Line B indicates the steady-state reached when the test solution mixes with bidistilled water. Line C is relative to the mixing of the extremely diluted solution with the test solution. Line D is obtained sending again solvent water in the two inlet tubes: it is the same as line A (baseline).All calorimetric experiments have shown that line C is higher than line B, thus indicating a more exothermic process, when the test solution is hydrochloric acid or sodium hydroxide. All other test solutions gave line B cohincident with line C.

3. Results

A preliminary study employing test solutions containing different solutes (ethanol, lactose, glucose, urea, sodium, potassium or lithium chlorides, sodium hydroxyde, and hydrocloric acid) put in evidence that only in the last two cases a heat is detected upon mixing with the extremely diluted solution, larger than that obtained when mixing the same test solution with bidistilled untreated water. In Table 1, the thermal excess (differences between the values corresponding to line C and line B, normalyzed according to eq.(1) are reported for the mixing of a series of samples prepared according to the described method , belonging to different lots, investigated at different times, and mixed with two different test solutions of sodium hydroxide and hydrocloric acid.

The most suitable concentration of the test solute has been looked for to evidentiate unequivocally the existence of the thermal excess in the described experimental conditions. To that, the mixing experiments, reported in Table 1, have been performed.

 Independently of the test solute, the thermal excess detected in the presence of succussed water with respect to bidistilled untreated water attains a constant value for a certain solute concentration (m) always in the range 0.001-0.005 mol kg-1. Then, to obtain the largest thermal effect in both cases, the most suitable concentration of NaOH or HCl is 0.01 mol kg-1. In tables I-X are reported the experimental excess heats of mixing of the extremely diluted solutions studied with NaOH and/or HCl 0.01m (mol kg-1). In table XI a summary of experimental results is reported.

4.Calorimetric titrations.

Very relevant information about the phenomenon under examination are drawn from a calorimetric titration of the extremely diluted solutions or, in general, of water treated according to the method described before.

A titration of the extremely diluted solution implies the determination of the thermal excess, with respect to the heat measured with water, when sodium hydroxide solutions at different concentrations are mixed with the samples under examination. Four titrations have been performed (Tables XII-XV of the Appendix), using four different samples of two different lots. Titration curves are qualitatively similar with a peculiar feature: two different plateaux appear (lines A and B of Fig. 2), with two different equivalent points, thus indicating the presence of two phenomena occurring successively. On the other hand, the heats of mixing, obtained with the reference solvent, behave, obviously, as the heat of dilution of the electrolyte NaOH (line C of fig:2). From these titration curves an equivalent points higher than 0.001 m (mol kg-1), could be determined. The same differencies come out from Fig.3, where the titration curve of treated water are reported, using a flow mixing vessel. Also in this case two phenomena are evidentiated, then it can be hypothesized that pH-dependent phenomena are present due to order-disorder transitions, related to modifications in the structure of the solvent induced by succussions and dilutions.

Fig. 2- Titration with NaOH. The curve reported is obtained using a batch titration vessel. Volume of the solution to be treated: 1.5 x 10-4 L. Concentration of titrating solution of sodium hydroxyde: 0.01m.

Fig.3- Titration with NaOH. The curves reported are obtained using a flow mixing vessel in assembly described in the text. mNaOH : concentration of the titrating solutions.

5.Conclusions

As a conclusion, a significant result has been attained: the mixing process with acids and/or bases produces a systematically exothermic excess as respect to the same process with bidistilled untreated water. Beyond that, the calorimetric titration curves unravel two pH-dependent phenomena, probably related to order-disorder transitions of the solvent water.

The overall features make to retain that succussions and/or dilutions can alter physico-chemical properties of water, probably transferring mechanical energy on the water, by a still now unknown mechanism: these changes can be detected by scientific commercial apparatuses (microcalorimeters), through experimental measurements of the heats evolved when mixing solutions under examination with acids or bases. It is worth to underline the very good qualitative reproducibility of the detected effects and their statistical relevance: that induces to study systematically the phenomenon. Work, in fact, is in progress with the aim of exploring the role and the importance of the three factors acting in the preparation of the extremely diluted solutions, namely succussion, dilution and nature of the initially present solute.

Acknowledgments

We thank drs. C. Santullo, G. Lanza and mr L. De Falco for support in organizing the work; dr. M. Cecchi from Sifra O., for the help in preparing the extremely diluted solutions; drs. M. Niccoli and F. Velleca for the help in experimental measurements.

References

1. J.J.Sawage and R.H.Wood,
J.Solution Chem., 5, 733, (1976)
2. C.Cascella, G.Castronuovo, V.Elia, R.Sartorio, S.Wurzburger,
J.Chem.Soc. Faraday Trans. I 86, 85, (1990)

Table I

H2O 3CH: mixing with NaOH 0.01m

1)Sample coming from a single preparation in 3 ml polypropylene container;

2)Sample coming from the mixing of ten preparations in 3ml polypropylene containers;

Manual succussion in dark glass containers,obtained througth a mechamical procedure that resembles the manual one; A Automatic succussion in polypropylene containers, througth an automatic procedure of pneumatic shaking; A+M Automatic succussion up to the (CH - 1)nth dilution and last succussion by manual succussion.

Table II
H2O 3CH: mixing with HCl 0.01m

1), 2) A, M and A+M as in Table I

Table III

H2O 30 CH: mixing with NaOH 0.01m

A, M and A+M as in Table I

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