NATURAL PHILOSOPHY. 191 



ably be facilitated if a short piece of iron or platinum tube of small diam- 

 eter were attached, which would displace less mercury, and prevent, to some 

 extent, a fluctuation of the column of mercury caused by the motion of the 

 balance. 3d. If very great accuracy is desired, it may be requisite that the 

 arms of the balance be symmetrical and bear equal and similar surfaces, so 

 that change of temperature or atmospheric pressure, the accumulation of 

 dust, oxidation of mercury, etc., may affect both sides equally. Variation 

 of temperature will cause an alteration in the diameter of the tube, and be 

 productive of a small error, for which no remedy is suggested. 



This instrument, it is obvious, may be so adjusted as to indicate the pres- 

 sure of the atmosphere in pounds and its parts on the square inch of surface. 

 But, as it will often be desirable to compare observations made by it with 

 those of other instruments, it will generally be required that it express the 

 height of the column of mercury ; to this end the instrument may be adjusted 

 to a pressure equal, say, to thirty inches of mercury at a temperature of 32 

 Fahr. If, now, a tube has been used having a capacity of 1000 grs. of mer- 

 cury at 32 F. for an inch of its length, which would have a diameter of 

 about '6 of an inch, each grain Avill represent the thousandth part of an inch; 

 and if a correction has been made for the capillarity of the tube, all its indi- 

 cations, at whatever temperature, Avill represent the height of the column 

 at 32 F., and require correction only for the altered diameter of the tube. 



A rude instrument has been constructed on the principle here indicated. 

 A barometer tube having a capacity of 100 grs. to the inch, or a diameter of 

 '18 inch, was suspended over the dish of a U. S. Post-office balance, upon 

 a peg, by turning which the tube was adjusted to the surface of the mer- 

 cury in the reservoir; and this rested upon the dish. Its operation was 

 such as to justify the foregoing conclusions. Of course a scale may be 

 attached, which will show, in the usual manner, the height of the column. 

 Silli man's Journal. 



MODE OF PREPARING LIQUIDS OF GIVEN SPECIFIC GRAVITY, 

 WITHOUT CALCULATION OR PREVIOUS TRIALS. 



In the laboratory and in the arts, we are often required to prepare a definite 

 mixture of two liquids, such as sulphuric acid and water, alcohol and water, 

 etc. One of two modes is generally employed. 1st. Given the quantity and 

 specific gravity of one of the liquids, the quantity of the other liquid is 

 calculated. This mode is not always practicable, requires time, and for 

 alcoholic liquids especially, the concentration or mixture gives rise to diffi- 

 culties frequently insurmountable ; or secondly, areometers are floated in the 

 liquors ; but this means, which is very practicable and very much used, pre- 

 sents great difficulties in manufacture, owing to the various temperature of 

 the mixtures. 



A densimeter of a new form, constructed by M. SpacoAvsky, of St. Peters- 

 burg, allows the preparation of a liquid mixture with great ease and pre- 

 cision, and without a thermometer. The apparatus consists of a vessel or 

 areometer of platina. This areometer is closed above by a very thin partition 

 or metallic plate, such as that employed in the aneroid barometers, and 

 yielding to the fullest pressure. At its lower end the areometer is terminated 

 by a tube furnished with a stop-cock. It is suspended by a platina wire from 

 one arm of a delicate balance, and equilibriated by a weight suspended also 

 by a platina wire from the other arm. The equilibrium thus established will 



