156 ANNUAL OF SCIENTIFIC DISCOVERT. 



trernity of the lever is a very fine spring, pointed at the end, 

 which rests upon the cjiinder and traces a white line upon the 

 black ground. At the end of each week the paper is changed for 

 a fresh one, the old one being prevented from having its record 

 destroyed by having a coat of varnish. The whole operation 

 takes but little time, including the attachment in a book, or, wdien 

 required, the record of one week to that of the preceding, so that 

 the indications may be continuous. The barometrical arrange- 

 ment of this instrument is far less liable to error than the ordinary 

 aneroid, where so many movements and accessories are required 

 to translate the changes of the barometric box to the indicating 

 needle on the face of the instrument. In order to render the in- 

 dication recorded useful for comparison, the paper can be divided 

 into equal parts, representing the days of the week, and again 

 subdivided to represent the principal divisions of the day ; this 

 has been done in practice, and instruments similar to what we 

 have just described have been in use some time, earning great 

 approbation for the fidelity and utility of the observations recorded 

 by them. — Scientific American. 



FREEZING MIXTURES. 



A remarkable mixture, discovered by Berzelius, for producing 

 intense cold, is the following: — 



Two or three pounds of chloride of lime is heated until it forms 

 a porous mass, and is powdered and passed through a sieve, by 

 which operation it absorbs just enough moisture as is necessary to 

 cause it quickly to dissolve in water. It is then mixed Avith half 

 its amount of snow in a wooden vessel placed in a mixture of 

 snow and salt. In the interior of this cooling mixture, mercury 

 or ether may be frozen when introduced in a platinum crucible or 

 glass ball. 



When this powdered chloride of lime is dissolved in half or 

 two-thirds its amount of cold water, it will easily freeze water 

 when introduced into the mixture in a proper vessel, and this may 

 perhaps finally be found a cheaper freezing mixture than any of 

 the common ones now in use, as by simple evaporation the origi- 

 nal salt may be regained. 



Other freezing mixtures are : — 



Mixtures. Parts. Descent of Thermometer. 



Carbonate of Soda, . . . 1 ^ 



Nitrate of Potash, .... 1 V 70" Fah. 



Water, 1> 



Chloride of Ammonium, . . 1} ^«o 



Water, ij **" 



Sulphate of Soda, .... 3 > l7/^o 



Water, 2 5 '" 



Nitrate of Ammonia, . . . 1 > -qo 



Water, 1 5 



As these mixtures are made simply with water, and not with 



