REPORT ON SOME CARBONIC ACID TESTS ON THEWEATHERING OF MARBLES AND LIMESTONES.By George P. Merrill,Head Curator, Department of Geology, United States National Museum.The tests registered below were made with a view of determiningnot merely the relative solubility of certam calcareous rocks used forbuilding and ornamental work, but as well, the manner in which thesolvent acted. The ultimate aim of the experiments, as is obvious,was to ascertam how the stones would withstand the effects of anatmosphere and its rainfall made acid through absorbed carbonicacid. To make the results appreciable within a reasonable time, itwas of course necessary to exaggerate the conditions. The processwas as follows : Two samples of each stone selected were cut into theform of cubes approximately an inch in diameter, though withoutany attempt at exact correspondence in weight. How close theapproximation is shown in the accompanying table of results.The surfaces of each cube were rubbed with flour of emery on a glassplate as smooth as the nature of the material permitted, but noattempt was made to polish. They were then thoroughly washedand dried at 100? C. The cubes were then suspended by threads, ineach case passed but once around the cube, in a large jar of waterkept acid by a stream of carbonic acid from a charged cylinder. Thewater was changed once each week. No attempt was made to havethe stream of bubbles constant and continuous, but the directionwas changed occasionally to make certain that aU were subjected tolike conditions. Twice during the trial the cubes were withdrawnand while still suspended dried out by artificial heat and againimmersed. At the end of 3 months they were all withdrawn, driedat a temperature of 100 degrees, and brushed off ^vith a soft fitch brushto remove any loosened granules or dust. The appearance of eachcube was carefully noted as to color changes as weU as to the mannerin which the solvent acted. The tables below give the weight of thecubes before and after and the loss of material both in weight andin percentage amounts. The first table gives the results of some pre-liminary tests which were not carried to completion, owing to imper-fection of apparatus. They are, however, included here, since sofar as they go they are confirmatory of those in the second. Theresults in both cases agree surprismgly weU. It will be noted thatwhile the amount of material lost in the first series is less than in thesecond, owing to the shorter period of trial, the two are always inaccord. The amount of material lost by solution is not, however,Proceedings U. S. National Museum, Vol. 49?No. 2108. 347
348 PROCEIWlNai^ OF THE NATTOyAL MT'^ilJCM. VOL. 49.the sole item of importance, nor indeed the item of most importance.It will bo noted that in some instances a stone losing a certain amountstill retains a nearly smooth surface and sharp arrises. Others becomeroughened, granules loosened to the point of falling away, and thearrises as a consequence left ragged. In some of the stones there isa tendency for the smaller interstitial crystals to disappear, leavingthe larger standing in relief. The Tennessee samples tested are ofthe gray and pink spotted varieties. In these tlie tinted calcite,which, judged from the forms, represents fragmental fossil material,is more refractory than the colorless and is left in slight relief. Inthe case of the oolitic limestones the oolites are eaten out, leavingthe crystalUne or interstitial material and the fossil fragments inrelief, the outline of the oolite being sometimes preserved by theinsoluble impurities. Tlie considerable amount of insoluble materialset free from these oolitic cubes during the trial settling to the bot-tom of the jar as mud or remaining to be brushed off the surfacewhen the cube was dried seems to have come wholly from the oolites,and not from the interstices. It will be noted, as might have beenexpected, that the dolomitic marbles were not appreciably affectedand that the oolitic stones lost during the trial an amount two andthree times as great as that of any other of the stones tested. Inbut one instance was there any marked change in color in any ofthe samities. TABLE I.PRELIMINARY TRIAL EXTENDING OVER PERIOD OF 70 DAYS.
Kind and localitv.
White crvstalline limestone:Marble, S'lilo, Colorado.White crystiilline liinpstonc:Marble, Picliens County, ( leor-gia.White c^^'stalline limestone:M!irl>lP, \VeRt Orovo, Penn-sylvania.rinlv crvstalline limestone:Marble, Knoxville, Tennessw.Gray crystalHne limestone:Marble, Concord, Tennftssee.White crvstalline limestone:Marble, Jutland, Vermont.Blue crvstalline linuvstone:Marble, "Jutland, Vermont.White crvstalline limestone:Marble, Carrara, Italy.White crystalline dolomite:Marble, Cbcl^evsville,MarylandWhite cr>-stallino dolomite:Marble, 'Piickahoe, New York.Oolitic limostono, Bedford, Indi-ana.
Oolitic limestone:Green, Kentucky. Bowling
Weightbeforetrial ingrams.
Or)3313393.5747
701,''.
4-IS.')
?178
/ 40. f>o:).''>\ 41.1245/ 44.444\ i\.0:Mj 3S.C. !().)\ 40. ,5885/ 38. SO\ ;!(i. 507/ 42.06.55\ 41.405/ 43.5785\ 41.1475
Weightaftertrial ingrams.
i f 41.1655\ 37. S355
44. 707543.881541.0,3542. 356546. 234544. ,58640. 90447.9725
40.118540. 43243. 83.5540. 589
.38. 11440. 05)2538. 775536. 485542.041541.379542. 243539. 8795
40. .50437. 1725
l.oss ofweightin grams.
0. 34550. 43250. 4,5850. 39050.11100.11.550. ,54450. .50550. 6310
0. ,5470. 6925-0. 6tV850. 46650. ,50250. 4960. 02;)0.02150. 02400. 02,551. 3351.268
0.61150. 663
Percent-age lossof weight.
0. 0077
. 0097
.011
.009
. 0024
. (M)2?
. 0108
.0104
.012
.013
. 016
. 015
.011
.013
.012
. (VK1t'.2
. (K)().58
. IKX)56
. 0(X)6
. 0304
. 0308
.014
.017
Heniarks.
Very slightly roughened; nogranulation.\Slightly roughened; nogranulation.
>l'"-fTect scarcely appreciable.(White portions slightlyetched, leaving the pinkstanduig in relief.White portions slight Ivetched, ioavinp the pinkstanding in relief.ISurfaces appreciably rough-/ ened.ISurfaces appreciably rough-/ ened: no granulation.ISurfaces appreoiablv rough-/ ened; like white kutland.Not appreciably acted upon.Not appreciably acted upon.Pistiiictlv roughened andpitted, the fossil fragmentsl(>ft standing in relief.Distinctly roughened andpitted," the oolites beingeaten out, leaving .sur-face covered by circularand oval pits often with aslight residual eminence iucenter.
NO. 2108. WEA TilBRING OF MARBLES AND LIMESTONES?MERRILL. 349TABLE II.SECOND TRIAL EXTENDING OVER PERIOD OF THREE MONTHS.
Kind of stone and locality. Originalweight ingrams Finalweight ingrams. IvOSS ofweight ingrams. Percent-age lossin weight. Remarks.
White crystalline limestone:Marble, Yule Creek, Colorado.White crystalline limestone:Marble, Pickens County, Geor-gia.White crystalline limestone:Marble, Cherokee Coimty,Georgia.White crystalline limestone:Marble, West Grove, Pennsyl-vania.White crystalline limestone:Marble, Proctor, Vermont.White crystalline limestone:Marble, Proctor, Vermont.White crystalline limestone:Marble, Pittsfield, Vermont.White crystalline limestone:Marble, Carrara, Italy.Gray crystalline limestone:Marble, Knoxville, Tennessee.Gray crystalline limestone:Marble, Knoxville, Tennessee.Gray crj'^stalline limestone:Marble, Knoxville, Tennessee.Pink crystalline limestone:Marble, Concord, Tennessee.White crystalline dolomite:Marble, "Cockeysville, Mary-land.White crystalline dolomite:Marble, Berkshire, Massachu-setts.White crystalline dolomite:Marble, Lee, Massachusetts.White crystalline dolomite:Marble, Tackahoe, New York.
Oolitic limestone, Bedford, Indi-ana.
Oolitic limestone. Bowling Green,Indiana.Oolitic limestone, Salem, Indiana
51.55148. 194
44. 03443. 667543. 388544.40047. 838547. 969544. 494544. 108544. 97445. 17242. 53643.97
43. 508542. 462
46. 79645. 172544. 06944. 30954.5. 716545. 556542. 734542. 963540. 72438. 435545.52945. 05243. 65944. 49343. 44244. 79246. 43847. 053
36. 094538. 3245
38. 437538. 684537. 279537.45
50. 646547. 2465
43.31542. 94642.733543. 68347.61547. 76843.6243.312543. 929544. 00141. 70542. 9715
42.59841.4885
45. 876544. 297543. 22643. 454544.5244.60941.80842. 167540. 687-38. 399544.838544. 37843. 62544.441543. 402544. 746546. 381547.0105
34. 49336.4495
37. 177537.4435. 3935. 591
0. 90450. 9475
0.7190. 72150.6550.7170.22350. 20150. 87450.7961.04451.1710.8310. 9985
0.91050.9735
0. 92450. 8750.8430. 8551. 19650.94750. 92650.7960.0370.036
0. 69050.6740.0340. 05250. 03950. 04550. 05750.0425
1.60151.875
1.261. 24451. 88951.869
0.017
.019
.0165
.017
.015
.016
.0047
.0042
.019
.018
.023
.026
.019
.022
.021
.023
.019
.019
.019
.019
.026
.021
.021
.0185
.00091
.00093
.015
.015
.00077
.0011
.00091
.0010
.0012
.0009
.044
.049
.033
.032
.0506
.050
[A very slight roughening ofthe surface, but no granu-lation and but slightly at-tacked on the edges orI arrises.
^Surfaces very slightly rough-/ ened, but no granulation.
^Surfaces very slightly rough-/ ened, a slight yellowing.\Surfaces roughened, but no/ granulation.Surfaces distinctly roughenedand granulated, small par-ticles loosened and fallingaway when handled orbrushed; arrises rough-ened.Surfaces distinctly roughenedand granulated, small par-ticles loosened and break-ing away when handled orbrushed; arrises stronglyattacked.Surfaces roughened by thecorrosion of the colorlessgranules leaving the pmktinted standing in relief.No granulation or mechan-ical loosening of particles.
>No perceptible change.(Surfaces distinctly roughenedby corrosion along planesof cleavage and colorchanged to a decided buff.|No perceptible change.No perceptible change.Surfaces much roughenedand pitted owing to solu-tion of the oolites leavingthe fossil fragments andcrystalline material of theinterstices in relief; arrisesstrongly attacked.The same, only that the stoneis more distinctly ooliticand the surface becomescovered with circular andoval pits.