602 REPORT — 1903. 



himself in a room with a kilogram of pure radium, because it would doubtless 

 destroy his eyesight, burn all the skin off his body, and probably kill him. 



It remains for me to express regret that without an undue extension of the 

 time devoted to this Address it would have been scarcely possible to afford 

 adequate treatment to the absorption spectra of inorganic compounds, particularly 

 those of the rare earths, and such also as afford evidence of the chemical constitu- 

 lion of saline solutions ; or of organic compounds closely related to coloured sub- 

 stances and dyes, the investigation of which leads to the elucidation of the origin 

 of colour, and serves to indicate the nature of the chemical reactions by which 

 coloured substances may be evolved from those which are colourless. 



Chemistry is popularly known as a science of far-reaching importance to specific 

 arts, industries, and manufactures ; but it occupies a peculiar position in this respect, 

 that it is at one and the same time an abstract science, and one with an ever- 

 increasing number of practical applications. To draw a line between the two and 

 say where the one ends and the other begins is impossible, because the theoretical 

 problem of to-day may reappear upon the morrow as the foundation of a valuable 

 invention. 



The following Papers and Reports were read : — 



1. AiTparatus for Determining Latent Heat of Evaporation. 

 By Professor J. Campbell Brown, D.Sc 



The apparatus exhibited furnishes a direct method of determining the latent 

 heat of evaporation, at the boiling point, of any volatile substance of which 

 something approaching 50 grammes can be obtained. None of the substance is 

 lost, and no comparison with any other substances is required. The amount 

 evaporated is accurately weighed and the amount of heat employed in evaporating 

 it is accurately measured. 



From 15 to 20 grammes of the substance are placed in a tube about 10 cm. 

 long and 2.3 mm. wide, which is closed at one end and drawn out at the 

 other end to an orifice 1-5 mm. wide. The tube contains in its lower third a 

 spiral of fine platinum wire welded at its extremities to thick platinum wire 

 terminals. These terminals pass through the bottom of the tube and dip into 

 mercury contained in U-shaped projections from the expanded neck of a flask of 

 30 to 50 c.c. capacity. This tube is heated to the boiling point of the liquid in the 

 manner about to be indicated and is then closed temporarily by a cap and care- 

 fully weighed. It is then replaced in the flask. A glass cap is ground on to the 

 neck of the flask, and is provided with an orifice through which vapour can escape 

 into an outer jacket. The space between the tube and the cap and neck of the flask 

 fornas the inner jacket. A long glass cap having an escape tube for the condensed 

 liquid is fixed over the whole expanded neck of the flask by means of a ring of 

 cork or indiarubber. 



A convenient quantity of the liquid is placed in the flask and boiled by a 

 suitable bath. Its vapour passes into the jacket above and raises the temperature 

 of the tube and its contents to the boiling point of the liquid. When the weighed 

 tube and its contents have been replaced and the temperature is constant, a current 

 of electricity is passed through the spiral by means of the mercury in the U-tubes, 

 The time is noted and an ammeter in the circuit is watched and recorded every 

 two minutes. A voltmeter is also switched into the circuit every two minutes 

 and read. At the end of, say, twenty minutes, the average amperes and volts are 

 recorded. From these data the heat "expended in evaporation is calculated. The 

 tube is taken out and re-weighed to ascertain the weight of substance evaporated 

 by this quantity of heat. The double jacket of its own vapour keeps the tempe- 

 rature constant at the boiling-point and prevents loss of heat into the room. 



The ammeter and voltmeter should be accurate to at least ^^^ of the total 

 reading employed ; and must therefore be more accurately calibrated than are the 

 best instruments usually supplied by the trade. 



The first experiments should "be rejected. With practice the results are 

 accurate and the method easy. The variations in different experiments by 

 different operators are usually a small decimal figuie. 



