236 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
cylinders, while, because of carbon in his smoky exhaust, the motor- 
ist himself is often regarded as a nuisance by the pedestrian. The 
householder thinks of carbon in terms of coal and sees the wood 
in his fireplace transformed to charcoal. ‘There was no romance 
in carbon to the London chimney sweep of a century ago, when 
little boys of five or six were sold for seven years for 30 shillings 
and forced up chimneys by their masters with slight regard for the 
danger of burning or suffocation. To these boys carbon became a 
personal matter, for many went unwashed for years. Even to-day 
the soot deposit over London amounts to 260 tons per square mile 
per year, and in many of our American cities the figure is undoubt- 
edly as high. Three days after a recent storm the surface snow 
taken from an average square yard in front of our Cambridge labo- 
ratory yielded 2.85 grams of soot and cinder, the equivalent of 934 
tons per square mile. In such amount and form carbon becomes 
a menace to health and property, a thing of loathing to a careful 
housewife, and a powerful incentive to the purchase of stock in 
laundry companies. 
The burning of coal is a principal cause of atmospheric dust, 
and over a city like London or Paris the number of dust particles 
per cubic centimeter of air may exceed 100,000, while over the 
oceans the air may hold only a few hundred per cubic centimeter. 
But the dust is not without its compensations, for to it we must 
ascribe the blue of the sky, much of the glory of the sunset, and, 
in large measure, the gentle precipitation of rain. 
CHARCOAL 
It was probably in the form of charcoal that man first became 
acquainted with carbon as he stirred in his cave the dying embers 
of his wood fires. With the soot from burning fat he drew pic- 
tures on his cave walls of the animals he knew, and very fresh and 
vivid some of these pictures still remain. Such great masters as 
Diirer, Holbein, and Michelangelo have since enriched the world 
by famous charcoal drawings, and soot has served as a vehicle for 
the communication of thought in the exquisite calligraphy of China 
as it serves to-day in printer’s ink. Manuscripts of Herculaneum 
written in carbonaceous ink appear unchanged after 1,800 years. 
Fortunately for our own standing with posterity, the fabric of our 
newspapers is far less durable than the ink it bears. 
Before it was displaced by coal there was a very general use of 
charcoal as a cleanly domestic and industrial fuel, but its chief em- 
ployment was in metallurgy and particularly in the smelting of 
iron. The reputation of charcoal iron still endures and is especially 
associated with that from Sweden. In England, timber for char- 
