TWELFTH ANNUAL YEAR BOOK— PART X 505 



pentlne In the bottom of the pail. The bristles should be submerged in 

 the liquid, but should not touch the bottom of the pail. If kerosene is 

 ustd ror cleansing, it should be removed by shaiviug the brush and rinsing 

 it in turpentine betore using again with paint. Brushes used with white- 

 wash or calcimine shouid simpiy be waslied and not put in the same 

 liciUids in wUicn the brusnes Ubed for oil paints are liept. If a brush has 

 been uscd lor shellac varnish it should be Kept in aicohol or in the var- 

 nish itsfcif. in general a varnish brush may be kept in the varnish in 

 wnich it is used. 



DBYING OF PAINTS. 



Water paints such as whitewash and calcimine dry in the ordinary 

 sense; lUui it>, L.y evaporation oi tne liquid, wuien in tne case oi tue two 

 piiiiiLS nifcUnou<-a IS vvatfcr. lue Uiyiug oi on paints, now ever, is quite 

 aiixcient, auu in oruer tu unucistanu tnis attention must be di'av\u to 

 Co-itaiu p^cuiiaiiLibS Oi tue bo-caiicU uryiug oiib. buppoae lour piatts of 

 giatos are eotit^u, one witii a tuin Uim oi water, auotuer witn feusoiine, 

 auutner witu a Ueavy miu>,rai on, aatl auotucr witu unseed on, a,a(l ail 

 lour piatt-b are eApobt-U to tne air lor severai days. Tne water ana gaso- 

 line vviii evaporate ana leave tue piates my auU practicany in tne con- 

 ttition in wuicu tuty were Ueiore appiyin^ tne liquid, 'lue piate covered 

 Wicn tne kcavy miaciai on win ue louud to oe srcasy, wnne the piate 

 CovcreU Witu nn&ceu oil wni aibo nave a coating on it, out tuis coat wnl 

 hist btcome tacii.y and Uiiany set to a haru, v arnisn-iiiie Uim. if tnis 

 expeiiiutnt IS tiica witn otucr ve&etaoie oiia, sucn as onve on, it win ne 

 fouiiU Luat bOiue oi tuem beuave very mucn iiive tUe mineral ons; tnat is, 

 tucic IS very biioUt tenueney towaru tne loimation oi a coating. UtUer 

 ons, bucu aa com and boy Ocan, win boUave in a manner siuiiiiir to tne 

 iiu£>i,fcU on; tnat is, tnere win ue tne loimation of a more or lebs tacto.y 

 mabs, witU pernaps tne hnai lormatiou ui a varnisn-iice material. i\one 

 Oi tne otuer Common ons, novvcver, wnl torm the varnisn-iiri.e coating so 

 rapiuiy, nor win tne coating be so hard as in the case of nnsced oil. 



Ons wnich beUave iiixe unseed oil are caned drying ons. it will be 

 seen irom tnis inu&tration, however, that tne term ■drying" as applied 

 to on IS not similar to the drying which taixes piace on tne exposure of a 

 material wet with water to tne dry air. The drying of a substance wet 

 witn water is reaily tne removal of the water by evaporation. The drying 

 of a drying oil is a change tailing place in the liquid. This change is 

 accompanied by an absorption of oxygen from the air, and the drying 

 does not tane piace in the absence of oxygen. It is hindered by moisture 

 and hastened by sunlight. 



The formation of this varnish-like film by the so-called drying of lin- 

 seed oil is an exceedingly important operation in the drying of oil paints. 

 Certain substances, compounds of lead and manganese, if dissolved in 

 the oil, hasten drying. Boiled oil which contains compounds of lead or 

 manganese, or both, will dry more rapidly than raw linseed oil. Instead 

 of using boiled oil, however, the drying of the oil in paints is generally 

 hastened by the addition of liquids known as driers. These liquids are 

 composed of compounds of lead and manganese generally thinned with 



