RURAL KN(;iNEKRING. 687 



lii«h .111(1 illO ft. long at the t-rt'st. caiialtk' of lioldiii},' hack 70(5.324 aci-e-f('«'t of 

 wator. Its object is not to raise the level of the water but to hold it hack 

 and reguhite the tlow, which, after passing down in its original bed for 220 

 miles, is diverted b.v a low weir into a distributing canal 132 miles long with 

 a branch 34 miles long. 



Irrigation and seepage experiment Uii>t. Vawnporr \I)i(Iia] Agr. Sta., 

 1907, i>it. (iil-7(). Jit/. 7).— This is a brief account of exiierimeiits being made to 

 ascertain the amount of water necessar.v for maize, wheat, and local crops. 

 Two tables furnish the data collected to date. 



Physical tests of Iowa limes, S. W. Rkykr {loiva Oeol. Survey Ann. Rpt., 

 i? (JHUd), PI). 91-150, pis. 20). — This article explains the difference between 

 white, brown, and argillaceous or siliceous limes; describes the processes of 

 sinking, setting and hardening, and the prejiaratitm of lime mortar; and I'e- 

 jiorts tests of mortars made with high-calcium white limes and magnesian and 

 dolomitic limes. 



The limes tested were high-grade products representative of pure white and 

 of magnesian or dolomitic lime. With such limes it was found, as a rule, that 

 the maximum strength is attained at the end of a setting period of to 9 

 months. "This is most pronounced where the higher percentages of sand are 

 employed. The notable exceiitions to this rule are found with the lowest sand- 

 lime ratios, the lower percentages of water used to slake, and are most con- 

 spicuous in the strongly dolomitic limes." Since carbonation occurs to only 

 a limited extent during the first (! or 9 months, the change which occurs during 

 the setting of mortar is considered to be largely the crystallization of the lime 

 hydrate. 



"In general, the greatest strength comes with the lower percentages of water 

 used in slaking. Equal amounts by weight of water and of dr.v quicklime give 

 in the majority of cases the highest results. Higher proportions are detri- 

 mental to tensile strength. This is more especially noticeable in the white 

 limes. ... As a rule, the highest strength is given by the lowest propor- 

 tions of sand, the curves being about equall.v divided between equal parts by 

 weight of sand and dr.v quicklime and two of sand to one of lime." The highest 

 strength was obtained with a 1 : 1 or 50 per cent mixture of lime and sand. 



"The whitt' limes recpiire more water to slake properly, generate more heat 

 In slaking, slake much more rapidly, and reduce to a more uniform paste than 

 the magnesian limes. The dolomitic limes set and harden more slowl.v but in 

 many cases attain strengths so much greater than do the white limes as to be 

 nlmost out of comparison. They will, therefore, stand gi'eater dilutions of 

 sand and still be sutliciently strong to meet the requirements of practical use." 



Modem silo construction, .7. P.. Davidson and M. Ij. Kino {Iowa Sto. Bui. 

 100, pp. '.).'i-l,'tO, fit/s. .'/.<). — This gives the results of investigations of existing 

 HJIos, and tlisciisses fiill.v the relation of construction to their failure or success, 

 as it was leariKMl that niaii.v of the failures were due to improper constructi<m. 

 In answer to circular letters reiiorts of KM silos were receivcnl and 111' silos 

 were examined by the junior author. 



It Is stated that the essentials of good construction require air-tight walls 

 and d<v»rs, walls smooth inside and rigid enough to withstand tlie pressure of the 

 silage, and an air space lietwwn tlie walls to prevent freezing. The proper lo- 

 cnlloii <'ontribiiles to the success of the silo, and the repoi'ts indicat<> that this 

 Hhould l)e outside of .-ill liuildings. A discussion of the dilTerent types ami their 

 e«»Kl includes silos of wood. Itrick, concrete, steel, cemeiit-ltlock, and stime. as 

 well as of common building tile, for wliicli there is a design submitted in detail. 



74921 -No. 7—09 7 



