White pine, Douglas fir, yellow pine, cypress, or any of these woods, usually contain some knots, which are sure to damage exterior white paint unless properly treated. These knots have a certain amount of pitch in them, which will penetrate through any oil paint and leave an ugly mark. They should be covered with shellac, which is not affected by the pitch. Shellac is a spirit varnish made from shellac resins dissolved in alcohol. The yellow shellac is the strongest, but the white is used where a light-colored paint is to be applied on top of it. The pitch which is so bad in knots is often distributed throughout the wood, as in Southern yellow pine, and this will often cause the paint to peel off. To prevent this to a certain extent, some specifications advise using benzol in the priming coat, in order to make the paint penetrate more deeply into the wood and get a better grip on the surface. The priming coat of any painting job should either be pure linseed-oil or linseed-oil with very little pigment in it. Its purpose is to fill the pores of the wood before the other coats are applied, for if an ordinary thick coat of paint were applied to raw wood, the surface would draw so much oil out of the film of paint that most of the pigment would be left dry and unfastened upon the outside. Only after the wood has been given the priming coat is it then time to putty up the nail holes and other defects, and not before, because the dry wood, as in the case of paint, will suck out the oil from the putty and leave it without anything to bind it together. The best putty for this work is made of linseed-oil with enough white-lead in it to make a thick paste. The putty which is commonly used, however, is made of whiting or ground chalk mixed with linseed-oil. This is durable if real linseed-oil is used, but often some inferior adulterant is substituted. After the holes are all puttied, the other coats of paint may be added. At least two good coats should be applied, and three coats give superior results. Plenty of time should be allowed between coats to permit thorough drying of the previous one. XVI LABOR-SAVING DEVICES FOR THE HOME _The Demand_