18(5 THE GEOLOGY OF MINNESOTA. 



[Qualitative tests. 



while others by a longer exposure to the same conditions would have shown still higher figures. 



Determination of the absorption of water by soaking. A third set of stones with an average 

 weight of about 70 grammes, approximately rectangular and measuring from an inch to an inch 

 and a half on a side, were dried in the hot-water hath to expel moisture. They were then cooled 

 in the desiccator and weighed. They were then placed in a large porcelain dish of water and 

 allowed to soak for four days. They were then severally taken from the water, and after the 

 water had been removed from their surface by pressing bibulous paper upon them, they were 

 weighed as expeditiously as possible to avoid loss by drying. The increase of weight is expressed 

 in percentage figures. The increase of weight thus shown, especially by several sandstones, is in 

 some cases very considerable. In other cases the absorption of water by soaking is scarcely greater 

 than the absorption from a damp atmosphere after the lapse of some weeks. 



Detei-mination of the action of carbonic acid. A set of pieces, similar in size and shape to 

 those used in the previous determination, were dried for six days at 2 12" Fahrenheit, then weighed. 

 They were then suspended by strings in a glass vessel of water, not in contact with one another, and a 

 stream of carbonic acid gas was run through the water for several hours at short intervals, so as 

 to maintain the water pretty well saturated. The gas was washed before entering the vessel con- 

 taining the stones. The water was changed every few days by use of a siphon. The action was 

 continued for six weeks. The stones were then soaked in pure water, wiped, dried at 212 F. for 

 six days and weighed. The loss of weight is given in percentage figures. Two glass vessels were 

 used in the experiment. The limestone pieces were placed in one, the sandstone and granite in 

 the other. The two were treated as nearly alike as possible. The stones suffered scarcely any 

 visible change. But the water in the vessel holding the limestones became highly impregnated 

 with carbonate of lime ; that in the other much less so. 



Determination of the action of strong acid fumes. Another set of pieces of stone, similar in 

 size and shape to the preceding, were dried for six days at 212 F., then weighed. They were then 

 placed in an apparatus similar to that used for determining the absorption of moisture, constructed 

 of glass and porcelain, the porcelain pan containing strong muriatic acid, and a bottle containing 

 nitric acid being placed within the apparatus, as also a bottle containing muriatic acid and black 

 oxide of maguanese, for the purpose of evolving chlorine. In this apparatus, exposed to the strong 

 fumes, the stones remained during seven weeks. They were then removed and placed in water to 

 soak, this water being repeatedly changed. When free from acid they were dried for six days as 

 at first, then weighed. The loss of weight is given in percentage figures. 



The design of this test was to determine the disintegrating and staining effects produced by 

 oxydizing agents, representing the action of the atmosphere intensified in degree and concentrated 

 in respect to time. 



Determination of the effect of frost. In this determination the pieces which had been used to 

 test the absorption of water by soaking, whose weight dry had been previously learned, were 

 placed in a shallow iron pan, nearly covered with water, and exposed outside the building in a 

 sheltered place to freezing and thawing from February 4th to April 1st, eight weeks To thaw, 

 they were occasionally brought into a warm room for a few hours. During the time stated very 

 little intense cold was experienced, but the water in the pan was in a frozen state nearly all the 

 time. After this exposure, the pieces were carefully examined, then dried for six days as usual 

 and weighed. The figures show the loss of weight caused by slight crumbling of edges, etc., by the 

 action of frost. 



Determination of the effect of heat. For this determination a muffle furnace was made use of. 

 The temperature of the muffle was raised to a red heat ; then the samples of stone, one after an- 

 other, were exposed to the heat of the muffle, being at first placed near the open mouth of the 

 muffle, then gradually moved inward until they came into the hottest part and were heated to red- 

 ness. Observations were made of the effect of the heating. They were lifted out with tongs once 

 or twice and closely inspected. After the heating test in the muffle, the pieces were severally 

 removed from the muffle and while still very hot, but at a temperature below red- 

 ness, they were immersed in a tank of water for a few minutes. The action of the 

 water, in crumbling or cracking the heated stones was observed and noted. The pieces 

 used were in size rather larger than those used in previous tests, being from one and a half 

 to two inches on a side for the most part. They had been well air-dried at the time this test was 



