Papers of other colours than green have been found to contain dangerous quantities of arsenic; thus blue, mauve, red, and brown may contain large quantities; the delicate greys often yield a considerable amount, and some white papers are heavily loaded with it. Arsenic is occasionally present in stockings and other wearing apparel, artificial flowers, toys, etc. In these cases, it may produce irritation of the skin, and even eczema. The presence of =arsenic may be detected= by the following tests:— (_a_) _Reinsch’s test._ A portion of the suspected paper (two or three inches square) is cut into small pieces, and placed in a good-sized test tube; water is added until the tube is about a third full and then one or two teaspoonfuls of pure hydrochloric acid, and a small piece of pure copper foil. If the test tube is now heated for a few minutes over a spirit lamp, arsenic, if present, will be deposited as a black or dark steel-coloured coating on the copper. A mere tarnish of the copper must not be accepted as evidence of the presence of arsenic, but an almost complete obliteration of the colour of the copper. (_b_) Take the copper covered with arsenic, dry it, and then heat it in a perfectly dry test tube. Crystals of white arsenic, which may be identified under the microscope, will be deposited higher up in the tube. (_c_) _Marsh’s test._ The ordinary apparatus for developing hydrogen by the action of diluted sulphuric acid on zinc is employed, the suspected paper being inserted in the bottle. The hydrogen coming off is burnt, and a clean porcelain surface is applied to the flame. If there is arsenic in it, it is deposited on the porcelain in a black patch. =Windows= are required to open directly into the external air in every habitable room. The window area according to the model bye-laws of the Local Government Board and the London Buildings Act of 1894, must be at least one-tenth of the floor area, and half of this at least must be made to open. The following rules have also been given. (B = breadth, L = length and H = height of room.) _Area of window_ (B × L)/10 _London Building Act_ (B × L × H)/100 _Gwilt_ √(B × L × H) _Morris_ In a room measuring 15 × 20 × 12 feet, the preceding rules would give a superficial area of window space of 30, 36, and 60 square feet respectively. Plate glass dissipates heat less quickly than sheet glass. Objection may be taken to plate glass windows, in passing, especially for shops, banks, etc., in view of the fact that they are commonly made without any arrangement for ventilation (see also page 148).