you allow 4 shillings a grain when the guinea is alloyed with silver, and but 2s. 10d. when the mixture is made with copper?

Father. Because the specific gravity of silver is much nearer to that of gold than that of copper; consequently, if equal quantities of silver and copper were mixed with gold, the silver would cause a much less loss by immersion in water than the copper.

As it seldom happens that the adulteration of metal in guineas is made with all copper, or with all silver, but generally with a mixture of both, three shillings is upon the average allowed for every grain that the base metal loses by immersion in water more then sterling gold.

Emma. There is a silver creamjug in the parlour; I have heard

mamma say, she did not think it was real silver: how could she find out whether she has been imposed on? Father. Go and fetch it. We will now weigh it.

Emma. It weighs 54 ounces, but I must weigh it in water, and it has lost in the water 10 dwts; and dividing 5 ounces, or 110 pennyweights by 104, I get for answer 10.7 the specific gravity of the jug.

Father. Then there is no cause for complaint, for the specific gravity of good wrought silver is seldom more than this.

wine at a tavern, and thrown the flask on the fire, he perceived that the few drops left in it were converted into steam; this induced him to snatch it from the fire, and plunge its neck into a bason of water, which, by the atmospheric pressure, was driven quickly into the bottle."

Emma. This was something like an experiment which I have often seen at the tea-table. If I pour half a cup of water into the saucer, then hold a piece of lighted paper in the cup a few seconds, and when the cup is pretty warm, plunge it with the mouth downwards into the saucer, the water almost instantly disap

pears.

Father. In both cases, the principle is exactly the same: the heat of the burning paper converts the water that hung about the cup into

CONVERSATION XVI.

Of the Hydrometer.

FATHER. Before I describe the construction and uses of the hydrometer, I will show you an experiment or two which will afford you entértainment after the dry calculations in some of our former Conversations.

Charles. The arithmetical operations are rather tedious to be sure; but they serve to bring to mind what we have already learnt, and at the same time show to what uses arithmetic may be applied.

Father. You know that wine is specifically lighter than water, and the

lighter body will always be uppermost: upon these principles I will exhibit two or three experiments. I have filled the bulb B with port wine to the

top of the narrow stem r. now fill a with water.

I

Emma. The wine is gradually ascending like a fine

A

x

B

red thread through the water to its surface.

Father. And so it will continue till the water and wine have changed places.

Charles. I wonder the two liquids do not mix, as wine and water do in a common drinking glass.

Father. It is the narrowness of the stem which prevents the admixture: in time, however, this would be effected, because water and wine have what the chemists call an attraction for each other.