162 



SCIENCE 



[N. S. Vol. XXXI. Xo. 7SS 



floats of itself on the surface and this burns 

 during the whole night. 



This night was observed all over Egypt 

 by the general lighting of lamps, and these 

 lamps were probably the forerunners of the 

 well-kno^Ti Greek and Eoman lamps of 

 clay and of metal which are so common in 

 onr museums. 



The candle and lamp were probably in- 

 vented very much earlier. We know that 

 both lamps and candles were used by the 

 priests of the Jewish temple as early as 

 900 B.C. The light of those candles and 

 lamps was due, as you know, to particles 

 of carbon heated in a burning gas. 



It is not fair to the chemists of our early 

 candle-light to skip the fact that great 

 chemical advances were made while candles 

 were the source of light, and so I touch for 

 a moment upon one of the early applica- 

 tions of chemical knowledge. The fats and 

 waxes first used were greasy and the light 

 was smoky and dull. They were capable 

 of improvement and so the following chem- 

 ical processes were developed and applied 

 to the fats. They were first treated with 

 lime, to separate the glycerol and produce 

 a calcium soap. This was then treated 

 with sulphuric acid, and the free stearic 

 and palmitic acids separated. These acids 

 were then made into candles and gave a 

 much whiter light than those containing 

 the glycerol ester previously used. Similar 

 applications of chemical principles are 

 probably known to you all in the refining 

 of petroleum. The crude distillate from 

 the rock oil is agitated with sulphuric acid 

 and then washed with a solution of sodium 

 hydroxide. This fact accounts, in consid- 

 erable degree, for the advance of a number 

 of other chemical processes. An oil re- 

 finery usually required the presence of a 

 sulphuric-acid plant in the immediate 

 vicinity, and this often became a source of 

 supply for other new chemical industries. 



Very great advances have been made in 

 the use of fats and oils for lighting pur- 

 poses, but there is so much of greater in- 

 terest in later discoveries that we will not 

 consider many of them. The distillation 

 of gas from coal or wood in 1739 was a 

 chemical triumph, and a visit to a gas plant 

 still forms one of the main attractions to 

 the young chemist in an elementary course 

 of applied chemistry. The first municipal 

 gas plant was established in London, just 

 about one hundred years ago. The general 

 plan, so apparently simple to us to-day, was 

 at its inception judged impracticable by 

 engineers. In spite of other methods of 

 illumination, the improvements in the 

 making, purification and application of 

 illuminating gas have caused a steady in- 

 crease in its use. Gas owes its illuminating 

 power to the fact that a part of the carbon 

 in it is heated to incandescence dui'ing the 

 combustion of the gas. It must contain, 

 therefore, such carbon compounds as yield 

 a fair excess of carbon, and this knowledge 

 has led to the schemes for the enrichment 

 of gas and for the use of non-luminous 

 water-gas as a base for illuminating gas. 



Various schemes were devised in the 

 early part of the nineteenth century for 

 using gas to heat to incandescence, rods or 

 surfaces of lime, zirconia and platinum. 

 This was not at first very successful, owing 

 to imperfect combustion of the gas. The 

 discovery of the Bunsen-burner principle 

 was made a little later. By thus giving a 

 much higher temperature to the gas flame 

 and insuring complete combustion, new im- 

 petus was given to this branch, and the 

 development of suitably supported oxide 

 mantles continued for half a century. 



Most prominent in this field is the work 

 of Auer von "Welsbach. It was a wonder- 

 ful series of experiments which put the 

 group of rare earth oxides into practical 

 use and started a line of investigation 



