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The freezing point degree of milk (FPD) is a classical indicator of cow milk quality. In camel milk, few references are available in the literature regarding the main factors of variation. In the present paper, two methods of FPD determination were used: the Reference method (RM) (using Cryostar) and the Express method (EM), using a milk analyzer (Milkoscan-FT1). The RM was used to determine FPD in 680 bulk raw or pasteurized camel milk samples. Regarding EM, 736 individual milk samples, 1323 bulk samples, 635 samples of pasteurized milk and 812 samples of raw milk used for cheese making were available. The variability of FPD was investigated according to month, lactation stage, milk composition, milk production and microbiological status. Correlations between methods were explored. FPD was highly correlated with most of the milk components and tended to decrease in cases of high contamination by coliforms or high total flora count. However, the weak significant correlations between the two methods indicated the necessity to specifically calibrate an automatic milk analyzer for camel milk.

Synopsis The unfrozen water content of various soils has been measured by calorimeter. The suction-moisture content characteristics of the same soils were also determined at room temperature, with conventional pressure plate and pressure membrane apparatus. Using the values of unfrozen water content measured during freezing, and the suction characteristics obtained during drying, a relation was found between the two sets of results. The relationship approximates that of Schofield, between suction and initial freezing point, of soils at various moisture contents. Knowledge of the relationship permits prediction of the amount of water remaining unfrozen in a soil at negative temperatures down to −1·0°C and often some what lower. Such prediction requires only determination of suction-moisture content characteristics by conventional methods together with a simple determination of the freezing point of an extract of the soil solution. In many cases, the accuracy of the prediction is apparently as great as can be obtained using even complex calorimetric methods. Using these relatively easily determined values of unfrozen water content at various temperatures, realistic estimates can be made of the apparent specific heats of frozen soils. The observed relationship provides a basis for studies of the effects of both load and temperature, on the proportions of ice and water in frozen soils and on the state of stress within the ice and unfrozen water. La teneur en eau non gelée de divers sols, a été mesurée par calorimètre. Les caractéristiques des teneurs eau-succion des mêmes sols furent aussi déterminées à la température ambiante, avec plaque conventionnelle de pression et appareil à membrane de pression. En utilisant les valeurs des teneurs en eau non gelée mesurées pendant la congélation, et les caractéristiques de succion obtenues pendant le séchage, un rapport fut trouvé entre les deux séries de résultats. Le rapport se rapproche de celui de Schofield, entre la succion et le point initial de congélation de sols de diverses teneurs en eau. La connaissance du rapport permet de prédire la quantité d'eau restant non gelée dans le sol à une température descendant jusqu'à −1·0°C et souvent quelque peu plus basse. Une telle prédiction nécessite seulement la détermination des caractéristiques de la teneur eau-succion par les méthodes conventionnelles, ainsi qu'une détermination simple du point de congélation d'un prélèvement de solution du sol. Dans beaucoup de cas, l'exactitude de la prédiction est apparemment aussi grande que celle qui peut être obtenue même en utilisant des méthodes calorimétriques complexes. En utilisant ces valeurs déterminées d'une manière relativement facile de teneur en eau non gelée à diverses températures, on peut faire des évaluations réalistiques des chaleurs spécifiques apparentes des évaluations réalistiques des chaleurs spécifiques apparentes des sols gelés. Les rapports observés fournissent une base pour les études des effets à la fois de charge et de température, sur les proportions de glace et d'eau dans les sols gelés et sur l'etat des contraintes dans la glace et l'eau non gelée.

The freezing point of soils is the boundary of change of physical state from a thawed to frozen condition. A paramount factor which affects the transition zone is the quantity and composition of the dissolved salt in the pore water. The marine soils used in the experiments were from the arctic coast with a range in the granulometric composition. The clay fraction consisted of 40% kaolinite, 30% montmorillonite, 25% chlorite and 5% quartz. Salts used were from soil extractions or from sea water. NaCl and CaCl[ 2] solutions were also used for artificial salination of the soil samples. The salt content used ranged from 0.2 to 1% by weight or in terms of the pore water was from 0.006 to 0. 055. Three stages were observed; a supercooling stage, a phase of comparatively constant temperature, and a gradual fall of temperature. The supercooling temperature was from 1.5 to 2 times the freezing point. Conclusions are as follows: (a) the grain size characteristics of the soil do not influence the freezing point when the moisture content is in excess of the liquid limit; and (b) when there are equal concentrations of the interstitual solution only the qualitative composition of the salts influences the freezing point. Within the range investigated the freezing point of the soil is inversely proportional to the molecular weight of the soluble salts.

Attention is drawn to the consequences of the finding that adsorbates are in a liquidlike state at temperatures below their bulk freezing point. If the relative pressure is based on the saturation vapor pressure of the undercooled liquid, differences between the N[2] and Kr surface areas and those between the BET and Dubinin-Raduskevich areas become minimal. On application of inappropriate relative pressure values in constructing isotherms, apparent supersaturation may be indicated.

Synopsis A property of water in porous materials is that it freezes at temperatures below 0°C. There is no single freezing temperature for water in soils. As ice is formed the freezing point of the decreasing quantity of unfrozen water falls further below 0°C. Latent heat of fusion is thus involved in temperature changes over a range extending to several degrees below 0°C. The latent heat and specific heat together constitute an apparent specific heat. Apparent specific heats for various silt, clay and organic soils have been measured in a calorimeter. The apparent specific heats generally rise as temperatures approach 0°C, and in a clay soil may be ten times as great at −1°C as at −5°C. The apparent specific heats for a given temperature depend on whether the soil is freezing or thawing, and on various other factors. The precise determination of heat quantities involved in temperature changes in soil in situ is difficult, mainly because of the several factors influencing the freezing of the soil moisture. Une propriété de l'eau dans les corps poreux est qu'elle gèle à des températures inférieures à 0°C. Il n'y a pas de température unique de congélation de l'eau dans le sol. Au fur et à mesure que la glace se forme, le degré de congélation descend au dessous de 0°C. Une chaleur de fusion latente est done en cause lors des changements de température couvrant plusieurs degrés au dessous de 0°C. La chaleur latente et la chaleur spécifique constituent ensemble une chaleur apparente spécifique. Les chaleurs spécifiques apparentes pour des limons, des argiles et des sols organiques divers ont été mesurées dans un calorimètre. D'une manière générale, la chaleur spécifique apparente s'élève lorsque la température s'approche de 0°C, et dans le sol argileux elle peut être dix fois plus grande à −1°C qu'à −5°C. La chaleur spécifique apparente pour une température donnée dépend soit du gel, soit du dégel du sol, et d'autres facteurs divers. La détermination précise des quantités de chaleur en cause lors des channements de température dans le sol, sur place, est difficile, surtout à cause de plusieurs facteurs qui influencent la congélation de l'humidité se trouvant dans le sol.

Adsorption of water has been studied extensively above 0 degrees C, but the problem of the phase transition of adsorbates in porous materials is presented at temperatures below 0 degrees C. Experiments that show how phase transitions modify length change-adsorption relationships are described. Adsorption-length change measurements from - 40 to -0.5 and isotherms at -20 and -0.5 degrees C were obtained. In another group of experiments different forms of isosteres were also obtained; the principle that water should be allowed to enter the sample at the low temperature was usually followed. Isotherms and length change- adsorption characteristics below 0 degrees C are qualitatively similar to those above 0 degrees C, but a decrease in adsorptive capacity and length change was observed. These results and those obtained from the isosteres lead to the conclusion that capillary condensation and menisci theories are operative and that a solid meniscus exists. It follows therefore that the saturated vapor pressure of frozen adsorbate is greater than that of bulk ice and that its volumetric expansion on freezing is similar to the bulk phase transition. It is shown how these phenomena can predict migration of water and generation of pressure within the porous body when it is subjected to cooling and warming cycles.

The system porous glass saturated with respect to water was studied in the temperature range +2 to -40 degrees. Calorimetric measurements with simultaneous observations on length changes revealed that two kinds of transformations took place at different temperatures below the normal melting point of bulk water. The amount of water that did not transform when this system was cooled to about -40 degrees is shown to correspond to approximately three monolayers. The experimental results suggest that the adsorbed water in porous glass even in the middle of the capillaries has a different state from that of bulk water, and it is concluded that the observed depression of the freezing point should be considered in terms of the different structure the adsorbate acquires from that of the bulk state.