BUILDING AND ORNAMENTAL STONES. 355 



louiid necessary to renew the coating every two or tlireo years, and 

 even then the results are unsatisfactory. 



Oil. — This, as stated by Julien,* always discolors a light colored 

 stone, while it renders a dark colored one still darker. According to 

 this authority the oil is applied as follows : The surface of the stone is 

 washed clean, and after dr;^ing is i)ainted with one or more coats of 

 boiled linseed oil, and tlually with a weak solution of ammonia in warm 

 water. This renders the tint more uniform. This method has l)eeu 

 tried on several houses in New York City, and the water-i»roof coating 

 thus produced found to last some four or live years, when it must be 

 renewed. 



raraffine.— This, dissolved in coal-tar naphtha, is spoken of,t but is not 

 recommended. A better method, as suggested by Julien,| consists in 

 l)rushing over the surface of the building with melted parafline and then 

 heating it gently until it has been nearly all absorbed into the pores of 

 the stone. This produces little or no discoloration, but it is thought 

 doubtful by some if the heating of the stone is not more iiijurious than 

 the paraflQne is beueticial. 



The preparation used in coating the Egyptian obelisk in Central 

 Park, New York, is said by Mr. Caflal§ to have consisted of parafldne 

 containing creosote dissolved in turpentine, the creosote being consid- 

 ered efticacious in preventing organic growtli upon the stone. The 

 melting point of the compound is about llOo Fahrenheit. In applying, 

 the surface to be coated is first heated by means of especially designed 

 lamps and charcoal stoves, and the melted compound applied with a 

 brush. On cooling it is absorbed to a depth dependent ui)on the degree 

 of penetration of the heat. In the case of the obelisk, Mr. Caftal states 

 that, in his belief, it was absorbed to the depth of half an inch. Some 

 OT-j' pounds of the material was used in going over the -J20 sipiare yards 

 of surface. An ecjual surface of brown sandstone is stated to require 

 ordinarily about 40 or 50 pounds. The cost of treating an ordinary 25- 

 foot brownstone front, with a porch, is given by this authority at from 

 $200 to $300. This process, like the last, has been objected to by some 

 on the ground that the heating was liable to injure the stone. Just how 

 much injury is likely to result from a temperature lower than that of 

 boiling water, it is perhaps yet too early to say. It seems scarcely pos- 

 sible that a good (piality of sandstone laid on its bed could be at all af- 

 fected; neither, it is safe to say, would brick. 



iSoft soap and alum solution. — This, as given by Julien, consists of 

 three-fourths of a pound of soft soap to 1 gallon of boiling water and 

 one-half a pound of aluin in 4 gallons of water. It is said to answer 

 well in exposed situations in England, but to require frequent renewal. 



* Teuth Ceusus, p. 389. 



t Notes oil buildiug construction. 



t Op. cit. 389-90. 



$ Trans. N. Y. Acad. Sci., Nov., 1885, p. GO. 



