45, CORNHILL, E.G., AND 122, BEGENT STREET, W., LONDON. 



Boiling-points under the pressure of an atmosphere. 



Centigrade. 

 Sulphurous Acid . . . . 10 



..Ether 37 



Bisulphide of Carbon ... 48 



Bromine 63 



Alcohol 78 



Distilled Water . . . .100 



Laws of Ebullition 



Centigrade. 



Turpentine 160 Q 



Strong Sulphuric Acid . . . 325 



Mercury , 350 ,, 



Sulphur 44? 



Cadmium 860 



Zinc 1042 



GANOT. 



I. The temperature of ebullition, or lolling point, increases with the pressure. 



II. For a given pressure, boiling commences at a certain temperature, which varies in, 

 different liquids, but which for equal pressures is always the same in the same liquid. 



III. Whatever be the temperature of the source of heat, as soon as ebullition begins the 

 temperature of the liquid remains stationary. 



Thus, the boiling point of water under the ordinary atmospheric pressure being 212 F. 

 or 100 Gen., it would not be heated beyond that point, whatever the intensity of the source 

 of heat ; the only effect of higher temperature being to hasten the rapidity of vaporisation ; 

 hence all the heat which passes from the source into the liquid is absorbed by the vapour 

 disengaged. 



SOLIDIFICATION OF OXYGEN. 



At the Royal Institution, May 27th, 1886, Professor Darwar exhibited for the first 

 time to a few friends, including the president of the Royal Society, the method he employs 

 for the production of Solid Oxygen. The successful device employed by the Professor at 

 the Royal Institution depends upon allowing liquid oxygen to expand into a partial vacuum, 

 when the enormous absorption of heat which accompanies the expansion results in the 

 production of the solid substance. Oxygen in this condition resembles snow in appear- 

 ance, and has a temperature about 200 Centigrade below the freezing-point of water. A 

 supply of this material will enable chemists to approach the absolute zero of temperature 

 and to investigate many interesting changes in the physical properties of bodies under the 

 primordial condition of the temperature of space. 



INSTRUCTIONS FOR FIXING OR SETTING HORIZONTAL SUN DIALS. 



It is most important that the plane upon which the Dial is to be fixed be truly horizontal, 

 and the North and South line be accurately ascertained. The surface of the Dial may 

 easily be made parallel to the horizon or level, with the aid of a good Spirit Level, by testing 

 its surface in at least three directions across its diameter. 



To find the true Geographical North and South or Meridian line for the place, it is 

 requisite to have a good Mariner's Compass, and also to know the Variation of the Compass 

 Needle for the locality at which the Dial is to be erected. For London the present variation 

 is Westerly 18 20' at Kew, 18 Greenwich. 



Now by the Compass bearings carefully mark off on the plane surface the true North 

 and South points, and by them set the Sun Dial to correspond. This will then indicate Solar 

 or True Time, which agrees with Mean Time (or that shown by a clock) only on four 

 different days in the year. To find the mean time it is necessary to apply a correction 

 called the Equation of J Time, from a table which is mostly engraved upon the best constructed 

 Sun Dials, or upon the wooden Artificial Horizon of Terrestrial Globes. Also see below. 



A convenient season for setting Sun Dials by this method is about the time of the Vernal 

 or Autumnal Equinox (March and September) when the Dial and clock very nearly agree. 



COMPASS VARIATIONS. From " Mechanics' Magazine? March I6tk, 1865. See p. 318. 



2o 



