or rather more than 4 shillings is to be deducted from the value of a guinea adulterated with silver, for every grain it loses by immersion more than standard gold.

Emma. How is that, Papa? Silver is much dearer than copper, and yet 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 than sterling gold.

Emma. There is a silver cream jug 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 5 ounces, but I must weigh it in water, and it has lost in the water, 10 dwts; and dividing 5 ounces, or 110 penny-weights by 101, 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

CONVERSATION XVI

Of the Hydrometer.

FATHER. Before I describe the con

struction and uses of the hydrometer, I will show you an experiment or two which will afford you entertainment, after the dry calculations in some of our former conver sations.

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 specif cally 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 в (Plate 11. Fig. 23.) with the port wine to the top of the narrow stem x. I now fill a with

water.

Emma. The wine is gradually ascending like a fine 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 x 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.

Here is a small bottle B (Plate 111. Fig. 24.) with a neck three inches long, and about one sixth of an inch wide; it is full of red wine. I will now place it at the bottom of a jar of water, a few inches