Directions for Measuring.—Reagents are measured in graduated cylinders (see Fig. 74). When the directions call for the addition of 5 or 10 cc. of a reagent, unless so directed it is not absolutely necessary to measure the reagent in a measuring cylinder. A large test tube holds about 30 cc. of water. Measure out 5 cc. of water and transfer it to a large test tube. Note its volume. Add approximately 5 cc. of water directly to the test tube. Measure it. Repeat this operation until you can judge with a fair degree of accuracy the part of a test tube filled by 5 cc. In the experiments where a burette is used for measuring reagents, the burette is first filled with the reagent by means of a funnel. The tip of the burette is allowed to fill before the readings are made, which are from the lowest point or meniscus. When reagents are removed from bottles, the stopper should be held between the first and second fingers of the right hand (see Fig. 75). Hold the test tube or receptacle that is to receive the reagent in the left hand. Pour the liquid slowly until the desired amount is secured. Before inserting the stopper, touch it to the neck of the bottle to catch the few drops on the edge, thus preventing their streaking down the sides of the bottle on to the shelf. Replace the bottle in its proper place. Every precaution should be taken to prevent contamination of reagents.
Fig. 76.—Microscope and Accessories.
1, eye-piece or ocular; 2, objective; 3, stage; 4, cover glass; 5, slide; 6, mirror.
Use of the Microscope.—Special directions in the use of the microscope will be given by the instructor. The object or material to be examined is placed on a microscopical slide. Care should be exercised to secure a representative sample, and to properly distribute the substance on the slide. If a pulverized material is to be examined, use but little and spread it in as thin a layer as possible. If a liquid, one or two drops placed on the slide will suffice. The material on the slide is covered with a cover glass, before it is placed on the stage of the microscope. In focusing, do not allow the object glass of the microscope to come in contact with the cover glass. Focus upward, not downward. Special care should be exercised in focusing and in handling the eye-piece and objective. A camel's-hair brush, clean dry chamois skin, or clean silk only should be used in polishing the lenses. Always put the microscope back in its case after using.
Experiment No. 1
Water in Flour
Carefully weigh a porcelain or aluminum dish. (Porcelain must be used if the ash is to be determined on the same sample.) Place in it about 2 gm. of flour; record the weight; then place the dish in the water oven for at least 6 hours. After drying, weigh again, and from the loss of weight calculate the per cent of water in the flour. (Weight of flour and dish before drying minus weight of flour and dish after drying equals weight of water lost. Weight of water divided by weight of flour taken, multiplied by 100, equals the per cent of water in the flour.)
How does the amount of water you obtained compare with the amount given in the tables of analysis?