V.)n} EUKAL ENGINEERING. 387 



Six systems of convict labor ai*e described as " the lease, the contract, the 

 piece-price, the public-account, the state-use, and the public-works-aud-ways 

 ;systems." The report embodies data obtained from personal visits made to 

 ■convict camps and conferences held with state highv^^ay and prison officials 

 in the States of New York, New Jersey, Virginia, West Virginia, North Caro- 

 lina, South Carolina, Georgia, Alabama, Florida, Mississippi, Louisiana, Texas, 

 Michigan, Colorado, New Mexico, Arizona, Utah, Wyoming, California, Wash- 

 ington, and Oregon. 



A special section is included on the character, preparation, and cost of food 

 from data prepared by the Office of Home Economics of the States Relations 

 Service. Other special sections on water supplies and camp sanitation are 

 included, nmch of the substance of which has been noted in previous reports 

 by Trullinger (E. S. R., 30, p. 690), Freeman (E. S. R., 34, p. 83), Lumsden, 

 Stiles, and Freeman (E. S. R., 34, p. 88), and Cook, Hutchison, and Scales 

 (E. S. R., 33, p. 455). 



Experimental studies of vacuum juice heaters, E. W. Kerr and S. J. Webre 

 (Lmiiskina Htas. Bui. 159 (1916). pp. 4^, figs. 20). — Experiments on the opera 

 tion of vacuum juice heaters, including the effect of air in steam, juice velocity, 

 absolute pressure of the heating steam, tube materials, and the length of vapor 

 path upon heat transmission, are reported. The experiments were made upon 

 three diffei'ent outfits, namely: (1) An especially designed small juice heater 

 coimected with a single effect evaporator in the engineering laboratory, (2) 

 vacuum juice heaters connected to each body of the double effect at the Audo- 

 bon Park sugar factory, and (3) the vapor juice heaters in connection with the 

 quadruple effect at the Central Florida in Cuba. The first outfit was used 

 .strictly for research work, while the other two represented operation under 

 regular factory conditions. 



Tlie laboratory experiments showed the marked effect of the presence of air 

 in steam in reducing the coefficient of heat transmission. " This shows the 

 necessity of properly venting vacuum juice heaters." The juice velocity was 

 varied from a minimum of 131 ft. per minute to a maximum of 502 ft. per 

 minute with corresponding variations in the coefficient of heat transmission of 

 from 412 to 588. Tests made to compare the coefficients of heat transmission 

 of copper and seamless cold-draAvn steel tubes with vacuums of 0.0, 6, 13, 

 and 18 in. and constant juice velocities gave average coefficients for copper and 

 steel tubes of 576 and 280, respectively. The greater the vacuum the lower was 

 the coefficient of heat transmission. 



In the experiments with the second outfit, the effect of air richness in the 

 heating vapor in decreasing the coefficient of heat transmission was shown. " It 

 was found to be impossible to control the removal of air through the vents 

 satisfactorily." Comparative studies of the effect of the use of juice and of 

 water on heat transmission showed that the coefficients obtained with juice 

 were considerably lower than those obtained with water. " The experiments 

 brought out very clearly the importance of thorough venting of air and drain- 

 age of condensation. The difficulties Aicountered in relation to these two points 

 emphasize the advantages, especially as regards the capacity, of taking the 

 heating vapors from other than the last body of a multiple effect, even though 

 the last body has the advantage in the matter of economy." 



Tests on the general performance of the vacuum heaters in the third plant 

 and on the effect of air in vapor showed that when provision was made for 

 venting air the coefficients of heat transmission were much greater. Tests on 

 the relation between air in steam and length of steam travel showed little 

 increase in air richness for the first 15 ft., but thereafter the increase was 

 81075°— No. 4—17 7 



