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John Dalton – Philosophical Experiments

CHEMISTRY

We must now proceed to describe the effects that are produced when bodies combine chemically. When this takes place, certain changes are produced in them, by which their appearance, and sensible qualities, are entirely altered. The “laws of combination," which cause these changes are exceedingly simple, and few in number ; yet they are capable of producing an extraordinary variety of effects. The experiments which follow will illustrate these laws; and the following particulars will, therefore, be useful in enabling the student to understand the manner in which they operate.

The first important fact to be noticed is, that when two substances combine, the compound they form is always different in its nature to themselves. Two bodies, decidedly poisonous, when combined chemically, may produce a compound, not merely uninjurious, but even necessary to our existence ! This fact is strikingly illustrated in the combinations of the two elements called oxygen and nitrogen. For example : —

• The atmosphere is a compound of ……Nitrogen4…...Oxygen 1.
• Nitrous Oxide (laughing gas) ……………..Nitrogen 2…..Oxygen 1.
• Nitric Acid (aquafortis)…………………….. .Nitrogen 2…..Oxygen 5.

Thus it will be seen, that the same elements which, when mixed together in the proportions first mentioned, produce the air we breathe, form one of the most active and destructive poisons, when combined in the quantities necessary to produce nitric acid ; for this acid and the air, it will be seen, are both formed from the same elements, only the proportions in which they are combined are different.

In the combinations of the element called carbon, or charcoal, we have another striking example of the different forms one substance can assume. Who would believe that a brilliant diamond, and a piece of common charcoal, are the same material, only in different forms? Yet such is the case; and the chemist has the power, by exposing the diamond to a great heat in oxygen gas, of reducing it to the state of charcoal. This circumstance may appear very extraordinary, but it is not more wonderful than that a piece of lump sugar may be converted into carbon. We have shewn, in the experiments which follow (experiment 115), the means by which this can be accomplished ; and it is, therefore unnecessary to allude to it more particularly.

A familiar example of the fact that, two bodies, actively poisonous in their natural state, may produce a substance, when combined, that shall be perfectly innoxious, is seen in our common table salt. This is composed of muriatic acid and soda. The muriatic acid, taken internally, causes much agony, and ultimate death ; and the caustic alkali (the soda), would produce effects very similar ; yet when combined together, they produce a substance ranking amongst the first necessities of life ; for, without common salt, it would be almost impossible to maintain health. As an example of poisons being produced from the combination of substances, which, in their natural state, are not injurious, we may instance the poisons which are formed by animals and vegetables. The dreaded worali—the poison used by the Indians—and the pestiferous and destructive upas, which is produced from the tree of that name, and to the influence of either of which animals cannot be exposed without the loss of life, are formed from the same elements as those which produce the luxurious fruits, and the wonderful variety of beautiful flowers that exist in the countries where these poisons are found.