double cyanides form with ammonia, and the crystals of many of the double cyanides. In 1837 he began a series of investigations of the liquid called Cadet's fuming arsenical liquid—the product of heating a mixture of acetate of potash and white arsenic, discovered in 1760—and brought out the radicle cacodyl, the first of a series of organometallic compounds which exhibit striking analogies with the metals. These bodies are unpleasant in every way, extremely poisonous, dangerously explosive, highly inflammable, and often, like cacodyl, insufferably offensive in odor. "It is difficult enough nowadays," says Professor Roscoe, in "Nature," "for a chemist to work with such substances, armed as he is with a knowledge of the danger which he has to encounter, as also with improved appliances of every kind to assist him in overcoming his difficulties. But Bunsen, forty years ago, was a traveler in an unknown and treacherous land, without sign-posts to guide him, or more assistance on his journey than was furnished by his own scientific acumen and his unfaltering determination. Nor did he escape scot-free from such a labor, for, in analyzing the cyanide of cacodyl, the combustion-tube exploded, Bunsen lost the sight of an eye, and for weeks lay between life and death, owing to the combined effects of the explosion and the poisonous nature of the vapor. 'This substance,' he writes, 'is extraordinarily poisonous, and for this reason its preparation and purification can only be carried on in the open air; indeed, under these circumstances, it is necessary for the operator to breathe through a long open tube so as to insure the inspiration of air free from impregnation with any trace of the vapor of this very volatile compound. If only a few grains of this substance be allowed to evaporate in a room at the ordinary temperature, the effect upon any one inspiring the air is that of sudden giddiness and insensibility, amounting to complete unconsciousness.'"
His next research, published in 1838, was into the chemical changes which occur in the blast-furnace. In it he showed that at least forty-two per cent, of the heat evolved from the fuel employed in the furnace was lost, and pointed out that a great economy might be effected by collecting the combustible gases which escaped, and saving them for subsequent use. The investigation led to the introduction of improved methods by which the waste gases were utilized, and the cost of the manufacture of iron was cheapened. The experiments made in this research were the first in which an accurate method of gas-analysis was employed, and entitle Bunsen to the credit of having introduced new and valuable processes in that line to chemistry.
In 1841 he invented the Bunsen battery, an apparatus which has come into general use as a scientific instrument, and in telegraphy. Its chief peculiarity is the substitution of carbon for copper or platinum as the negative pole.
He visited Iceland in 1846-'47, and devoted special attention to the study of the volcanic phenomena of the island, particularly of the