6o 



SCIENTIFIC NEWS. 



[May and, li 



promotes the removal of the products, and insures a suffici- 

 ent indraught of air for the complete combustion of the gas ; 

 it also minimises the effect of a down-draught. The fol- 

 lowing particulars are given by the makers : — 



Tai/e III. giving particulars of gas-heated boilers. 



For very small boilers, gas at 3s. per 1,000 cubic feet will 

 not cost more than the average expense of a coal or coke 

 fire, if account be taken of the waste and the attendant's 



time. For larger sizes, however, the cost will be in favour 

 of fires ; but with gas it is much more easy to regulate the 

 temperature, and no attendance is necessary. 



When hot water is used for heating buildings, it is neces- 

 sary to have in each room one or more coils or groups of 

 piping to give a sufficient surface from which heat can be 

 radiated. Some examples of these are given in the follow- 



Fig.28. 



ing Illustrations: — Figs. 32 and 23 show the elevation and 

 section of a horizontal coil, and Figs. 24 and 25 of a verti- 

 cal coil of simple construction. Fig. 26 is a radiator, made 

 by Mr. J. Keith, which is built up of vertical sections bolted 

 together, and shaped so as to give as large a radiating sur- 



face as possible. It is well designed for its purpose. Fig. 

 27 is a vertical section, and Fig. 28 a sectional plan of a 

 coil made by Mr. J. Weeks, in which an air pipe, open at 

 both ends, is inserted through the middle of each hot-water 

 tube. In this way the heated surface exposed to the air is 

 largely increased. 



POISONS IN THE HOUSEHOLD. 



WE are not for the present about to discuss the mysteries 

 and the iniquities of secret poisoning, or to re-open 

 the causes cc'lebres of the bunglers Palmer, Dove, and Tawell. 

 Our task is less melodramatic and more useful. We wish 

 to call attention to some of the poisons with which modern 

 civilization brings us into contact, and which, through care- 

 lessness and ignorance, find their way into our food, our 

 drink, and even into the air we breathe. 



Foremost must stand lead, a metal which may be called 

 the meanest and the most treacherous of poisons. If it is 

 introduced gradually into our bodies. Nature " gives no 

 sign." We may go on day by day absorbing more and more 

 of the poison, and when we at last become aware that we 

 have an enemy within us it may be too late. Yet we use 

 this metal or its alloys for lining cisterns, for water-pipes, 

 for taps and funnels, for the so-called tinning of cooking 

 utensils, for the capsules of bottles, and for packing up 

 articles of food. 



We must give a momentary glance at some of these items. 

 Water-cisterns are altogether to be condemned from a sani- 

 tary point of view, and their lease of life will run out as 

 soon as the constant-supply system is introduced. But, 

 where they are necessary, no lead should be used in their 

 construction. The London water-supply, indeed, has, prac- 

 tically speaking, no appreciable action upon lead, and may 

 stand in vessels or flow through pipes of that metal without 

 becoming poisoned. But the pure waters of the North of 

 England — preferable in every other respect — take up so 

 much lead as to become very dangerous. Our readers may 

 perhaps remember the details of an action brought against 

 the Corporation of a town in Yorkshire by a professional 

 gentleman, whose health had been entirely ruined by lead- 

 poisoning. It is therefore satisfactory to know that Mr. 

 Crookes, Professor Odling, and Dr. Tidy have devised a 

 practical method of lining lead water-pipes with a safe 

 protective material. 



Meantime, where the water-supply is " soft," it is a wise 

 precaution to let a few quarts run away at the tap before 

 filling the kettle. 



In tinned saucepans, etc., there is no danger so long as 

 the material used is really tin, since tin, though a strong 

 poison if dissolved, is not acted upon by ordinary articles of 

 food. Unfortunately, pure tin is now discarded in favour of 

 an alloy of tin and lead, which readily yields to the acid 

 juices of fruits and vegetables. French cooks are particu- 

 larly desirous of seeing the insides of their utensils well 

 coated with this objectionable alloy, la claire, as they call it ; 

 hence we need not wonder that chronic lead-poisoning is 

 more prevalent in France than it is even with us. Fortu- 

 nately the quality of the " tinning " of a saucepan may be 

 detected by means of a simple test. If the inside is rubbed 

 with a piece of white paper, this should not be soiled ; if it 

 is blackened, lead is surely present. 



The thin, very thin film of tin lining and coating the cans 

 and boxes in which Australian meats, sardines, etc., are sold 

 sins in the same manner, as does also the tin-foil used by 

 confectioners. Of course the quantity of lead than can be 

 introduced at once into a man's body, through these and 

 similar channels, is infinitesimal, but the process goes on 

 silently and slowly, and at last the critical point is reached. 



