In commenting on Prof. Hartley’s paper, Mr. Laurie said he had never used linoleate of manganese for boiling with oil, but by the use of borate one did get a boiled oil paler than the oil with which one started. If you take linseed oil which has been already bleached in the sun to a golden yellow, and convert it into boiled oil with manganese, a further bleaching process undoubtedly takes place. An oil prepared with manganese salts, spread on a glass plate, and allowed to dry in the dark, will remain almost colourless, whereas if it were boiled with a lead salt it quickly darkens, even if it is kept away from impure air. Even in a dark room, in pure air, a picture painted with oil boiled with lead will darken. That is another argument in favour of manganese, and he should say it ought always to be used in preparing oil for artistic purposes. CHAPTER XIII. PAINT MACHINERY. In Fig. 40 is shown a complete set of paint grinding and mixing machinery, made by Wright & Co., 157 Southwark Bridge Road, London, S.E., which has given highly satisfactory results in efficiency and economy. It has a set of three granite rollers 30 inches by 15, and two mixing cylinders or pugs, 24 inches in diameter by 25 inches deep, the whole mounted on a strong cast-iron frame. It is made in the following five sizes:-- ---+----------------+---------+---------+----------+------------------------- | | | | | Work turned out per day. No.| 3-roller Mills.| Diam. of| Speed of| Weight. +------------+------------ | Size of Roller.| Pulleys.| Pulleys.| (Approx.)| Ordinary | White | | | | | Colours. | Lead. ---+----------------+---------+---------+----------+------------+------------ | in. in. | in. | | cwt. | tons. | tons. 1 | 16 × 9 | 18 | 70 | 12 | ½ to ¾ | 1½ 2 | 22 × 12 | 24 | 60 | 16 | 1 “ 2 | 4 3 | 22 × 14 | 26 | 55 | 22 | 3 “ 4 | 8 4 | 30 × 15 | 30 | 50 | 30 | 4 “ 5 | 10 5 | 36 × 16 | 30 | 50 | 35 | 5 “ 6 | 12 ---+----------------+---------+---------+----------+------------+---------- The utility of having the pug mills placed above the granite rollers is to save labour and space, and the roller mill is kept constantly at work. There are two pugs, one of which is always ready to deliver to the rollers, whilst the other is getting ready by the time the first is being emptied; by this means the output is always going on, and hence great saving both of time and labour. The pugs are [Illustration: Fig. 40.--WRIGHT’S PAINT MILL.] easily fed from a wooden stage fixed to the frame at the back of pugs. The drawing shows the gear driven by a cog-wheel, but if required it can be driven by fast and loose pulleys. The whole of the machine is very compact.