200 REPORTS ON THE STATE OF SCIENCE.—1917. 
oxide with lime and that you can displace carbonic gas from limestone by 
eulphurous oxide and also by phosphoric oxide; and as you know that sulphuric 
acid acts on limestone, you will be prepared to argue that sulphuric oxide can 
also combine with lime. Phosphoric oxide has proved to be stronger than 
sulphurous oxide—try whether sulphuric or sulphurous oxide be the stronger, 
in a similar sense, 
Contrast sulphurous with sulphuric acids. The fact that sulphuric oxide 
proves to be the stronger is clearly of interest in justification of the name 
sour-stuff, or oxygen ; the stronger and more pronounced acid being that which 
contains the major proportion of oxygen. 
Aquafortis,—There is no doubt that, in early times, as soon as the alchemists 
found a new substance, they tried its effect on all the substances with which 
they were acquainted. In this way, when they discovered oil of vitriol, besides 
finding out more or less by accident if not by carelessness that it was very 
corrosive and destructive of their skin and clothes, they probably very soon 
tried what action it would have on substances such as nitre or saltpetre and 
sea salt. The former often appears in the form of crystals on the soil in the 
neighbourhood of manure heaps; saltpetre occurs in large quantities in Chili in 
certain districts where there is no rain to wash it away. Both kinds of salt- 
petre are very valuable as manures. When vitriolic acid is added to saltpetre 
and the mixture is gently warmed in a retort, a very volatile and acid liquid 
distils over, the retort becoming full of brownish vapour. ‘his liquid is very 
corrosive, staining the skin a deep yellow. Of course, the alchemists tried 
the action of this acid on everything at hand, metals such as gold, silver, 
copper, lead, tin, zinc and iron, and found that it dissolved all but gold : as it 
was much stronger than the other acids they knew, they called it aquafortis. 
To the present day, the jeweller uses aquafortis to distinguish spurious from 
real gold. 5 
Aquafortis—or nitric acid as it is called on account of its formation from 
nitre—you have learnt, is used in converting sulphurous into sulphuric acid; 
it must therefore be capable of giving off oxygen and must contain an oxide. 
Nitre, or villainous saltpetre, as Hotspur calls it in Shakespeare’s ‘ Henry IV.,’ 
has been used for centuries past in making gunpowder—a mixture of charcoal, 
sulphur and nitre; also in fireworks. The modern explosives—gun-cotton and 
nitroglycerin—are also made with the aid of nitric acid. What happens when 
gunpowder is fired—in what way do charcoal or sulphur and nitre interact? 
Try to find out. 3 
Muriatic acid.i-We get back to the kitchen and our own food once more 
when we come to salt. Oil of vitriol acts upon it at once—fizzing takes place 
and an acid fume escapes—spirit of salt, the old alchemists called it. They 
were clever enough to find out that this fume is very soluble in water and 
the solution is known to the present day by the oil-and-colour man, the plumber, 
and in kitchen regions, as spirit of salt. It is used in cleaning and removing 
scale from baths, closet pans, etc. You will find that it is very acid and that 
it stains tne clothes but is not corrosive like oil of vitriol and aquafortis. The 
plumber uses it in soldering, after ‘killing it’ with zinc—everyone should 
learn to solder, and it may be worth your while to take the hint given by the 
plumber and see if you cannot follow up the clue. What is the action of the 
oil of vitriol on the nitre and salt? You know that it displaces the carbonic 
gas from limestone stuff—is its action on the salt and nitre a similar one—are 
they comparable with limestone stuff? 
The zinc, you find, is readily acted upon by the muriatic acid—examine the 
product and compare it with similar substances which you have prepared pre- 
viously ; it will be well to fit up apparatus which will enable you to prepare it 
at will, at any desired rate. Contrast it with coal gas and determine very 
carefully what is formed from it when it is burnt. 
When this inquiry is complete, you should recognise that you have made 
a discovery of the greatest importance with reference to your previous work 
and to the nature of foodstuffs such as starch. Again, you have an illustration 
of the fact that information is to be gained from the most unexpected quarters 
—who would suppose that the plumber could help you to determine the com- 
position of starch? 
a 
