[13] Page 62. _Common salt_, or chloride of sodium, crystallises in the form of solid cubes, which, aggregated together, form a mass, which may be broken up into the separate cubes. [14] Page 62. _Iceland_ or _Calc Spar_.--Native carbonate of lime in its primitive crystalline form. LECTURE III. [15] Page 79. _Solution of a Salt._--Acetate of soda. A solution saturated, or nearly so, at the boiling point, is necessary, and it must be allowed to cool, and remain at rest until the experiment is made. [16] Page 86. _Binoxide of Nitrogen and Hypo-nitrous Acid._--Binoxide of nitrogen is formed when nitric acid and a little water are added to some copper turnings. It produces deep red fumes as soon as it comes in contact with the air, by combining with the oxygen of the latter to form hypo-nitrous acid. _Binoxide of nitrogen_ is composed of two parts oxygen and one part of nitrogen; _hypo-nitrous acid_ is composed of one part of nitrogen and three parts of oxygen. LECTURE IV. [17] Page 106. _Chlorate of Potash and Sulphuret of Antimony._--Great care must be taken in mixing these substances, as the mixture is dangerously explosive. They must be powdered separately, and mixed together with a feather on a sheet of paper, or by passing them several times through a small sieve. [18] Page 107. The mixture of chlorate of potash and sugar does not require the same precautions. They may be rubbed together in a pestle and mortar without fear. One part of chlorate of potash and three parts of sugar will answer. The mixture need only be touched with a glass rod dipped in oil of vitriol. [19] Page 107. _Two Salts Dissolved in Water._--Sulphate of soda and chloride of calcium. The solutions must be saturated for the experiment to succeed well. [20] Page 111. _Lead Pyrophorous._--This is a tartrate of lead which has been heated in a glass tube to dull redness as long as vapours are emitted. As soon as they cease to be evolved, the end of the tube is sealed, and it is allowed to cool. [21] Page 115. _Gun-Cotton_ is made by immersing cotton-wool in a mixture of sulphuric acid and the strongest nitric acid, or of sulphuric acid and nitrate of potash. [22] Page 115. _Paper Prepared like Gun-Cotton._--It should be bibulous paper, and must be soaked for ten minutes in a mixture of ten parts by measure of oil of vitriol with five parts of strong fuming nitric acid. The paper must afterwards be thoroughly washed with warm distilled water, and then carefully dried at a gentle heat. The paper is then saturated with chlorate of strontia, or chlorate of baryta, or nitrate of copper, by immersion in a warm solution of these salts. (See _Chemical News_, Vol. I., page 36.) LECTURE VI.