204 Master Minds of Modern Science 



unusually busy during the past few years. They always 

 are when trade is bad, for often a fire is the only way to 

 stave off bankruptcy. Petrol has always been the main- 

 stay of the fire-raiser. The old trick was to fill a bladder 

 with petrol and hang it over a lighted lamp. Within an 

 hour or so the heat caused the bladder to explode ; then 

 blazing petrol was scattered all over the room, and 

 everything was instantly afire. 



But Science soon outwitted the fire-bug. After fires 

 that aroused suspicion, Government chemists tested small 

 fragments of paper, carpet, or cloth, and by steam- 

 distilling were able to discover whether petrol had been 

 used to start the flames. Their greatest triumph was 

 when the only relics brought them after a fire of this kind 

 were some fragments of celluloid. The celluloid was not 

 merely charred, it was burned; yet even so they were 

 able to decide that it had been in contact with petrol. 

 Thus was revealed the most ingenious device yet adopted 

 by the professional fire-raiser, who in this case had strewn 

 the floor of the doomed building with celluloid balls filled 

 with petrol. His guilt was clearly proved, and instead of 

 pocketing the insurance money he received a sentence of 

 three years' penal servitude. 



It is hard to believe that less than a hundred years ago 

 water was pumped direct from the Thames near Hunger- 

 ford Bridge for the use of Londoners. Small wonder that 

 cholera swept the city and that people died in thousands 

 from typhoid and similar diseases. The fall in Great 

 Britain's death-rate is due as much to the provision of 

 pure drinking-water as to all the great improvements in 

 medicine, and one of the tasks of the Government chemists 

 is to keep an eye upon the purity of water-supplies. 

 Country districts require these services more than great 

 cities, which have their own municipal analysts. We all 

 owe a very great debt to the late Sir Edward Frankland 

 (President of the Royal College of Chemistry in 1865) 



