410 ARCHITECTURAL SCIENCE TEACHING. 



lacy that the dam is necessary to prevent the patient's breath moistening- 

 the gold, thereby preventing cohesion. The gold is more liable to be soiled 

 from other causes ; as for instance, the operator's breath, sultry atmosphere, 

 coal gas, carbonic acid gas, smoke from the annealing lamp, and sulphurous 

 fumes from the rubber. 



I use the dam only when obliged to, and have no difficulty, in a majority 

 of cases, in keejDing the cavity perfectly dry by means of napkins and 

 other simple and unannoying aj^pliances. I filled teeth twenty-five years 

 ago with "soft gold," by means of smooth instruments, that are in perfect 

 condition to-day, and I have no hesitation in asserting that the "rubber 

 dam " and " mallet " are used seven times in ten to the disadvantage of both 

 patient and operator. 



TECHNOLOGY. 



ARCHITECTURAL SCIENCE TEACHING. 

 ELEMENTARY CLASS. 



Question. — Describe different materials used by painters. Describe ingredi- 

 ents of color. — The materials used by painters are paints, oils, driers, stains, 

 varnishes, etc. Colors or paints maj^ be divided into five classes, according 

 to their principal ingredients. Lead paints, most commonly used, have 

 white lead or carbonate of lead as a basis. This material is ground up in oil 

 in a stiff paste. Linseed oil, with litharge or other driers, and sometimes 

 turpentine, are added to it to form the paint ready for use. The required 

 tint is obtained by adding to this the proper coloring pigment. The exact 

 proportion of ingredients is regulated by the nature of the work, climate, 

 etc. Eed lead enters into the composition of the priming coat because it is 

 a good "drier" and sets "hard." Linseed oil is used as a medium for apply- 

 ing the paint; it fills up the wood pores, and acts as a preservative. Tur- 

 pentine makes the paint easier to work, and more liquid, but it plays no part 

 in the preservation of the wood, as the greater part evaporates. Driers are 

 mediums to cause the contained oil to dry and set quickly. Various mate- 

 rials are used, as litharge, sugar of lead, etc. Zinc paints have zinc oxide as 

 a basis. Silicate paints are manufactured from almost pure silica, which is 

 not acted upon by any metal or acid — in fact is almost indestructible. This 

 kind possesses the advantages of great durability, has no galvanic action 

 when applied to iron, as in the case of lead paint, and does not tarnish by 

 the action of gases. Colors are made same as the lead paints, and are mixed 

 in the same way. Oxide of iron paint acts as a good preservative for iron- 

 work. Bituminous paints are used for a similar purpose, and for rough 

 carpentry. Stains are mixtures used to darken wood to the color of the im- 

 itated wood. Varnishes are of various kinds — copal, etc. — and are used tO' 

 preserve the paint, and give a gloss to the finishing coat. 



