NOTES 639 



on the cleaning and restoration of museum exhibits. Dr. Scott spent some 

 eighteen months working in a temporary laboratory at the British Museum, 

 testing methods for dealing with a great variety of exhibits, including prints, 

 enamels, articles of silver, lead, iron, and copper, and lichen-covered pre- 

 historic rock paintings. Among some of the methods he describes may be 

 mentioned the apphcation of pure hydrogen peroxide to lead paints blackened 

 by the action of the sulphuretted hydrogen in the atmosphere, by suspending 

 the blackened surface about an eighth of an inch above a block of plaster of 

 Paris which has been sprinkled as evenly as possible with a concentrated 

 solution of the peroxide. The action of the vapour is, of course, slow and the 

 exposure should last for some hours. Another neat device is that for the 

 preservation of cracked enamels by keeping them in an oil-pump vacuum 

 for about half an hour, covering them with a 10 per cent, solution of dried 

 Canada balsam in benzol, and finally letting in the air so as to force the balsam 

 into the cracks. The enamel is then left in a vertical position to drain and dry. 



We have already referred in these notes to the work of Dr. Margaret 

 Fishenden on the radiant efficiency of various kinds of domestic grates. 

 Technical Paper No. 3 of the Fuel Research Board describes the further 

 experiments intended to test the usefulness of the low temperature carbonisa- 

 tion coke cakes from the Greenwich Fuel Research Station for sitting-room 

 fires and various types of kitchen ranges. The experimental methods were : 

 (i) to determine with a Richmond radiometer the radiant heat passing 

 through a surface 12 in. square opposite the centre front of the fire and 

 34-4 in. away ; (2) to compare, with a thermopile, the radiation over a 

 hemisphere of 34-4 in. radius round the centre of the fire. These observa- 

 tions permit the total amount of radiant heat to be measured. The ratio 

 of this total to the calorific value of the coal burnt gives the " Radiation 

 Efificiency " of the fire. As before, the old-fashioned register grate with the 

 space beneath the bars boxed in by a fender with adjustable doors and a plate 

 flue damper proved itself more efficient than any of the modern barless grates 

 which were tested, and this both for coal (efficiency 24-2 per cent.) and coke 

 cakes (308 per cent.). Further, the coke cakes in every case gave better 

 results than coal. The experiments on kitchen ranges lead to the conclusion 

 that it is impossible to design a range which will perform the three entirely 

 separate functions of water heating, oven heating, and room heating simulta- 

 neously without a serious diminution in the efficacy of all three. We 

 recommend this report to all those who are interested in the domestic heating 

 problem, especially if they are thinking of alterations in their own homes. 

 It may be obtained from H.M. Stationery Office, Imperial House, Kingsway, 

 W.C.2, price gd. 



We have now received the full report on Heat Insulators by the Engineering 

 Committee of the Food Investigation Board. An abstract of the results has 

 already been given from the pages of the annual report of the Board. A 

 study of the full data now published shows that cork, slagwool, charcoal and 

 wood fibres, when of good quality and dry, have practically the same thermal 

 conductivity, viz. : o-oooii cal. per sec. per cm. per i°C. This suggests that 

 the resistance these substances offer to thermal conduction is not very far from 

 the limiting value that is practically obtainable by subdividing the air space. 

 (The thermal conductivity of still air is 0-00005 c.g.s. units.) The only sub- 

 stance to give better insulation than these is rubber expanded by gas into a 

 highly cellular form (density o-o6 to 0-12 gm. per c.c.) by vulcanisation under a 

 high pressure {e.g. 100 atmospheres), which is gradually released in the cooling 

 down stage so that the gas distributed through the rubber expands and gives 

 it an unbroken cellular structure. The conductivity of this material is about 

 0-000085 c.g.s. units. An appendix to the Report contains a detailed account 

 of an ingenious calorimeter for finding the specific heat of insulating materials 

 which cannot be heated to 100° C. on account of the resulting alteration of 



