An objection might be raised that with such an apparatus the temperature in every part of the bath may not be uniform, and so the temperature of the dye-liquors in the pots might vary also, and differences of temperature often have a considerable influence on the shade of the colour which is being dyed. This is a minor objection, which is more academic in its origin than of practical importance. To obviate it Mr. William Marshall, of the Rochdale Technical School, has devised a circular form of dye-bath, in which the temperature in every part can be kept quite uniform. The dyeing laboratories of Technical Schools and Colleges are generally provided with a more elaborate set of dyeing appliances. These in the latest constructed consist of a copper bath supported on a hollow pair of trunnions, so that it can be turned over if needed. Into the bath are firmly fixed three earthenware or porcelain dye-pots; steam for heating can be sent through the trunnions. After the dyeing tests have been made the apparatus can be turned over and the contents of the dye-pots emptied into a sink which is provided for the purpose. Many other pieces of apparatus have been devised and made for the (p. 214) purpose of carrying on dyeing experiments on the small scale, but it will not be needful to describe these in detail. After all no more efficient apparatus can be desired than that described above. Dyeing experiments can be made with either yarns or pieces of cloth, swatches as they are commonly called; a very convenient size is a small skein of yarn or a piece of cloth weighing 5 grammes. These test skeins or pieces ought to be well washed in hot water before use, so that they are clean and free from any size or grease. A little soda or soap will facilitate the cleansing process. In carrying out a dyeing test the dye-pot should be filled with the water required, using as little as is consistent with the dye-swatch being handled comfortably therein, then there is added the required mordants, chemicals, dyes, etc., according to the character of the work which is being done. Of such chemicals as soda, caustic soda, sodium sulphate (Glauber's salt), tartar, bichromate of potash, it will be found convenient to prepare stock solutions of known strength, say 50 grammes per litre, and then by means of a pipette any required quantity can be conveniently added. The same might be followed in the case of dyes which are constantly in use, in this case 5 grammes per litre will be found strong enough. Supposing it is desired to make a test of a sample of Acid Red, using the following proportions, 2 per cent. dye-stuff, 3 per cent. sulphuric acid and 15 per cent. Glauber's salt, and the weight of the swatch which is being used is 5 grammes, the following calculations are to be made to give the quantities of the ingredients required:-- For the dye-stuff, 5 (weight of swatch) multiplied by 2 (per cent. of dye) and divided by 100 equals (5 x 2) / 100 = 0.1 gramme of dye.