[4] Pages 23 and 24. _Power or Property in Water._--This power--the heat by which the water is kept in a _fluid_ state--is said, under ordinary circumstances, to be _latent_ or _insensible_. When, however, the water changes its form, and, by uniting with the lime or sulphate of copper, becomes _solid_, the heat which retained it in a liquid state is evolved. [5] Page 23. _Anhydrous Sulphate of Copper_: sulphate of copper deprived of its water of crystallisation. To obtain it, the blue sulphate is calcined in an earthen crucible. [6] Page 29. _Add a little liquid to the marble, and decompose it._--Marble is composed of _carbonic acid_ and _lime_, and, in chemical language, is called _carbonate of lime_. When sulphuric acid is added to it, the carbonic acid is set free, and the sulphuric acid unites with the lime to form sulphate of lime. _Carbonic acid_, under ordinary circumstances, is a colourless invisible gas, about half as heavy again as air. Dr. Faraday first shewed that, under great pressure, it could be obtained in a liquid state. Thilorier, a French chemist, afterwards found that it could be solidified. LECTURE II. [7] Page 55. _Crystallisation of Alum._--The solution must be saturated--that is, it must contain as much alum as can possibly be dissolved. In making the solution, it is best to add powdered alum to hot water as long as it dissolves; and when no more is taken up, allow the solution to stand a few minutes, and then pour it off from the dirt and undissolved alum. [8] Page 57. _Red Precipitate of Biniodide of Mercury._--A little care is necessary to obtain this precipitate. The solution of potassium should be added to the solution of perchloride of mercury (corrosive sublimate) very gradually. The red precipitate which first falls is redissolved when the liquid is stirred: when a little more of the iodide of potassium is added, a pale, red precipitate is formed, which, on the further addition of the iodide, changes into the brilliant scarlet biniodide of mercury. If too much iodide of potassium is added, the scarlet precipitate disappears, and a colourless solution is left. [9] Page 57. _Paper Coated with Scarlet Biniodide of Mercury._--In order to fix the biniodide on paper, it must be mixed with a little weak gum water, and then spread over the paper, which must be dried without heat. _Biniodide of Mercury_ is said to be _dimorphous_; that is, is able to assume two different forms. [10] Page 59. “_Prince Rupert’s Drops._”-These are made by pouring drops of melted green glass into cold water. They were not, as is commonly supposed, invented by Prince Rupert, but were first brought to England by him, in 1660. They excited a great deal of curiosity, and were considered “a kind of miracle in nature.” [11] Page 60. _Thick Glass Vessels._--They are called _Proofs_ or _Bologna phials_. [12] Page 61. _Mica._--A silicate of alumina and magnesia. It has a bright metallic lustre--hence its name, from _mico_, to shine.