earlier chapters of this book indirectly teach the principles of qualitative analysis, but the authors' plan has obliged them to assume that at certain stages of his progress the student has become acquainted with the ordinary processes of qualitative and quantitative analysis. Appendices are added, containing (1) the outlines of experiments bearing on the work done in Part I., (2) tables which may help the student in performing the analytical parts of the easier experiments, (3) numerical data frequently used in the laboratory. M. M. PATTISON MUIR. CAMBRIDGE, October, 1887. COURSE OF PRACTICAL CHEMISTRY. PART I. CHAPTER I. CHEMICAL AND PHYSICAL CHANGE. Exp. 1. Hold a piece of platinum wire in the flame of a Bunsen-lamp for a few minutes. Then hold a piece of magnesium ribbon in the same flame. The platinum becomes red-hot, glows, and emits light; when removed from the flame, it presents the same appearance as before it was heated. The magnesium also glows; but in addition to this, it is burnt: a white powder is produced, unlike the magnesium; this white powder is called magnesia. The change produced in the platinum was a physical change. The change of magnesium to magnesia was a chemical change. Exp. 2. Magnetise a knife-blade, by drawing the poles of a horseshoe magnet over it several times in the same direction. Bring the magnetised blade close to a quantity of iron-filings; the iron is attracted to the blade. The steel which forms the blade has acquired a new property, but it still exhibits all those properties which characterise steel. Place some iron-filings in a porcelain basin, and add some dilute sulphuric acid; when effervescence has ceased, add a little more acid, then evaporate until the liquid becomes slightly thick, but take care that the whole of the iron has not M. P. C. 1 disappeared; filter while hot, and allow the greenish coloured liquid which runs through the filter-the filtrate—to cool. Green crystals of sulphate of iron are formed as the liquid cools. Compare these crystals with the iron-filings with which you began the experiment, as regards colour, appearance, hardness, and solubility or insolubility in water; the green crystals are evidently quite a different kind of matter from the iron. The change produced in the knife-blade was a physical change. The change of the iron to sulphate of iron, by causing it to interact with sulphuric acid, was a chemical change. By the process of filtration, a liquid is separated from a solid. The liquid which runs through the filter is called a filtrate. Exp. 3. Heat a little iodine in a large dry test tube, heating only that part of the tube where the iodine is. The iodine slowly changes to a dark violet vapour, but as this comes into contact with the colder parts of the tube, a solid body is formed; this solid is easily seen to be the same as the iodine before it was heated. The change of a solid to a gas, followed by the re-formation of the solid on cooling the gas, is called sublimation. Heat a little dry powdered lead nitrate in a dry test tube. A reddish-brown gas, called nitrogen tetroxide, is formed, and a yellowish-white solid, called lead oxide, remains. The action of heat on the iodine has been to produce a physical change. The change of lead nitrate to lead oxide and nitrogen tetroxide, produced by the action of heat, has been a chemical change. Exp. 4. Dissolve a little common salt in water,* in a porcelain basin; place the basin on the top of a beaker, of a size such that part of the basin is within the beaker; put a piece of paper between the beaker and basin; put some hot water in the beaker and place it over a lamp. (Fig. 1.) As the water boils the steam surrounds the basin and heats its contents nearly to 100o. The water in the basin is thus evaporated, without danger of the solid matter, which is formed as the Fig. 1. water passes away, being lost by spirting. When the contents of the basin are dry, collect some of the * Always use distilled water. |