BUILDING AND OKNAMENTAL «TONES. 33.'> 



I'reeziiijj;' lempi'iatiuvs upon fstones s;itur;it(,'(] witii uioistuic At a Ilmii 

 peratuie of .KP Falir. tlie j>n\ssuio exerted h.y walc' passiiiij,- iVoiii a li(jiii<l 

 to a solid state ainoimts lo not leys than 138 tons to tlie stinan; Coot, or 

 as I'rotessor Geikie has stiiUiu.^ly pur it, is e(jnal to the weiyht of eol- 

 unm of ice a unle high. Is it, then, astonishing" that a j)orons sandstone 

 exi)osed in a house-l'iont to be saturated by a winters rain and then, 

 snbjccted to tenii)eratures j>erha})s several <legrees l)elo\v the iVeezing 

 point sliows signs of weakness and exfoliation after a single season's 

 exposure f 



Since, then, as every (juarry man kiufws, iu> stone, liowever shong, 

 can eixlure the enormous strain to which it would be subject if fro/en 

 solid when holding any considerable amount of water conlined wiihin 

 its ])ores, it is but natural to conclude, as a matter of course, that otliei' 

 things being e(jua) those stones are most durable which will a.bsori)and 

 retain the least moisture.* 



This rule is not to be accepted, however, without a considerabl-.' giain 

 of allowance, since a coarsely j)orous stone, though capable of taking 

 up a large anujunf of moisture will also j)art with il readily, or ii' frozeii 

 while saturated Avill permit a considerable ])roportiou of tiic ex[>ansi\e 

 force of the solidifying water to l)e expeiuled otherwise lliai' in i)ush- 

 ing a}>art tbc grains composing ir. (Otherwise expressed, the water will 

 freeze out of u coarsely porous stone, winle in one that is com[)act it 

 may create sad havoc. This is well illustrated by the common occur- 

 rence of water freezing in straight cylindrical or widelyexpaudiug ves- 

 sels, and in uarrow-uech(Ml ])itchers and bottles. In the first instance 

 the opeu space above is suilicieut to allow all the expansion to take 

 place vertically. The lutrrow-necked vessel, on the other hand, is almost 

 invariably broken. 



To ascertain, then, the porosity or ratio of absor})tion of any sti>ne is 

 an important test.t 



Obviously the best method of ascertaining the power of a stone; to 

 withslan<l the eli'ects of liost is to actually expose prei)ar('d Ijlocks to 

 such a temperature, wiien saturated with water, as to freeze them st)lid 

 and then note the amoum of disintegration, or loss in strength. Un- 



* •' Otlicr things being (U|n;il, it may prol)abl3' l)(5sai(l liiat the vulno of a stone Coi- 

 Ijuilding ])urposL's is invcrstly as ils poiosity or al)sorI)ing powci-." (Hunt, Cliuin. 

 and Gcol. Ksstiys, p. Kil.) 



tflunt ill a SL'iic'8 of tests olitaiiicd results as follows: 



Potsdam sandstone, Canada, abi-orbed iVoin ('.50 to li.'Jti i)er eent. in twenty-four 

 Lours. 



Medina sandstone, Canada, absoi lied iVoiii '.\.'M (o 1.04 per eent. in twenty-lour 

 hours. 



yub- Carboniferous saiidslone, Ohio, absorbrd iVoin '.l.f/.l to 10. 'J2 [)er cent, in twenty- 

 four hours. 



Lower Silurian iiniestoin\s ;!nd doloniiirs, Canada, .-ibsoibed from 0.11 to ;").!'>.'') ])er 

 eent. in twcnty-iour lioiirs. 



Tertiary limestones, (.'aeii, I'ranee, abforlx-d from l.'> to Ki.d.") j)er ei'iit. in twenty- 

 four hours. 



