8 Mons. C. Despretz o?i the Maxhmim Density of Liquids. 



or seven points, which I sought to render fixed. In order to 

 avoid the influence of the warming or cooling of the vessel, 

 thermometers containing mercury and saline solutions were 

 taken alternately. A curve was traced with the apparent 

 contractions and expansions, to which was drawn a tangent 

 parallel to the line of expansion of the glass. The tangential 

 point gave the temperature of the maximum, i. e. the point 

 where the expansion is equal to the contraction of the glass, 

 which is evidently the point where the absolute dilatation of 

 this solution is zero. This is the transition of the contraction 

 into the expansion by cold. 



M. Despretz did not find a single aqueous solution which 

 did not show a maximum either above or below the freezing 

 point. The solutions which contain I to 3 centimetres of 

 foreign matter are in the first predicament ; those containing 

 more, in the latter. 



Every one can demonstrate the existence of a maximum for 

 any aqueous solution whatever; for this purpose it is only ne- 

 cessary to construct a thermometer with the solution, and to 

 lower the temperature rather slowly: the liquid is seen to 

 contract down to a certain point, and then by a continued 

 refrigeration regularly to expand. 



These experiments being very long and laborious, after 

 having proved the existence of a maximum for any aqueous 

 solution, the author contented himself with extending these 

 researches to eleven different substances : sea water, chloride 

 of sodium, chloride of calcium, carbonate of potash, carbon- 

 ate of soda, sulphate of potash, sulphate of soda, sulphate of 

 copper, and alcohol. 



With the exception of sea-water, every substance was dis- 

 solved in pure water in seven different proportions. These 

 ten substances therefore give seventy solutions. The nature 

 of the substances was varied, in order to follow the general 

 course of the phaenomenon. Among them were delicjuescents, 

 efHorescents, bodies which are not affected by the air ; some 

 very soluble, others of little solubility. 



We will begin with mentioning the results which relate to 

 sea-water. I first operated, says M. Despretz, with an artificially 

 formed sea- water according to Marcet's analysis; but M.Arago, 

 to whom I mentioned my first experiments, had the kindness to 

 offer me some sea-water collected by iVl. Freycinet in the 

 Southern Ocean. This water weighed at 20° l°-0273. The 

 mean from twelve experiments gave — 2°*55 for the tempera- 

 ture of the freezing point in a state of agitation ; at the in- 

 stant of freezing the thermometer returned to — 1°*84 of 

 density. This fluid has its maximum density at — 3°*67. 

 This is the mean deduced from five experiments with three 



