Front matter
BOUGHT WITH THE INCOME FROM THE
SAGE ENDOWMENT FUND
THE GIFT OF
Preface
The matter contained within these pages is broadly that which is taught, under the direction of Professor Corfield, in the Practical Hygiene Course at University College. It is hoped that the book will prove of value to those interested in Public Health, and to those seeking Public Health degrees, and that it may be read along with the many excellent works upon Hygiene and Public Health which are now in circulation, but which of necessity deal with the subject of hygienic analyses in far too cursory a manner.
An effort has been made to convey to the reader, in a concise and practical form, the knowledge necessary to enable him to make those analyses which may be fairly considered to be included within the domains of practical hygiene. To treat the subject exhaustively would necessitate a very bulky volume, and those who recognise the breadth of subject matter embraced by the title " Public Health Laboratory Work," will appreciate that it has been found necessary, in the present volume, to avoid all discursive matter save what is' required to make the rationale of a process evident, and where there are several processes in vogue to one common end, to select that one which experience has taught to be at the same time the most simple, ready and efficient — to the exclusion of all others.
It has not been an easy task, in every case, to decide as to what should be included and what omitted.
VI PREFACE.
There are, for instance, several recent and somewhat improved methods of estimating the carbonic acid in air, but the process of Pettenkofer has become what one may term " classical," and is that which is still generally asked in Public Health Examinations ; and since the method is sufficiently accurate, when carefully performed, for all practical purposes, it was thought advisable to introduce it to the exclusion of others.
The subject of hygienic analysis will be seen to dovetail itself into the work of the Public Analyst, but not to such an extent, it is held, as to render that officer any the less essential to a district.
The writer acknowledges his great indebtedness to the useful contribution on bacteriological methods by Dr. Boyce, for he recognises how much this enhances the value of the work ; he desires also to express his thanks for many kind and valuable suggestions from Professor Corfield, Dr. Louis C. Parkes and Dr. Braga.
He is further indebted to Dr. Louis C. Parkes for the use of figures 51, 52, 55, 58, 60 to 67, 69 to 74, 81, 82, 84, 88, 89, go, taken from his " Hygiene and Public Health."
H. R. K.
University College, W.C.
Chapter I. Page
The fitting up of a laboratory for water analysis . . . i Weights and measures upon the metrical system ... 14 Tables of solubilities and atomic weights 16
CHAPTER n, A water report 17
CHAPTER HI.
The collection of samples 21
CHAPTER IV.
The physical characters .... -29
CHAPTER V.
Organic matter in water 34
CHAPTER VI.
Wanklyn's process • • 39 via
LABORATORY WORK.
CHAPTER VII.
The oxidisable organic matter, estimation of Tidy's modification of the Forchammer process .
PAGE.
CHAPTER VIII.
Dr. E. Frankland's process 67
CHAPTER IX.
Oxidised nitrogen in nitrates and nitrites 72
Qualitative tests for nitrates 75
Qualitative tests for nitrites 76
Quantitative estimation of nitrites 77
Quantitative estimation of nitrates and nitrites ... 78
CHAPTER X.
Qualitative test 85
Quantitative estimation 86
CHAPTER XI.
The poisonous metals gi
Qualitative tests 93
Quantitative estimation 98
CHAPTER XII.
The non-poisonous metals ....
. 104
Lime
. 104
Magnesia
■ 105
. 106
Sulphates
. 107
Phosphates
. 108
CONTENTS. IX
CHAPTER XIII.
PAGE,
The solid residue no
Quantitative estimation 112
CHAPTER XIV.
Quantitative test for temporary and pernlanent hardness . 125
Hardness due to magnesium salts . » . . . 127
CHAPTER XV.
Examination of the sediment . 130
Chemical examination ....... 130
Microscopical examination 131
CHAPTER XVI.
Gases in water 139
Analysis of mineral waters .... . 141
The opinion upon a water analysis 142
CHAPTER XVII.
A very pure water 146
A foul and dangerous water 147
A suspicious water 148
Rain water . . 149
A typical peaty " upland surface " water .... 150
Spring water from the' chalk 151
A typical rain water 151
A deep well water from the chalk ... . 153
Sea water 153
Sewage 154
Scheme for effecting an analysis in the quickest and most convenient manner 154
LABORATORY WORK.
Scheme for examination purposes . . • • An analytical form for mineral residues
"Alkalimetry and acidimetry
Table of atomic weights (by latest researches) .
A quick method of estimating the " nitrogen in nitrates '
PAGE.
156 161
CHAPTER VIII. The characters of the air collected from various sources
• 231
Marsh air . .
. 231
Sewer air
. 232
Air over burial grounds . . . . •
. 232
The air of mines
• 233
The air during fogs
• 233
Ground air . . •
■ 233
Xll LABORATORY WORK.
PART V. Food Examination
CHAPTER I.
The milk of diseased cows 265
CHAPTER H.
The analysis of milk 267
The physical characters ....... 267
The specific gravity 272
The total solids and the ash 275
Solids, fat and non-fat 276
The lactoscope 279
CONTENTS.
xm
Chapter VII. Page
The average composition of Other cereals and the pulses . . 325
Oatmeal 325
Arrowroot 325
Sago 326
Cornflour 326
Lentil flour 327
Pea meal 327
Bean meal 327
Rye meal 327
Barley meal . 328
Potato flour 328
Ground rice 328
The microscopical characters of the different starch granules,
CHAPTER VIII. Meat 341
The characters of good meat 343
The characters of bad meat 345
Opinion to be formed with regard to condemnation . . 349
The important parasites of flesh 355
Cysticerci 355
Trichina spiralis 317
Actinomycosis 361
Distoma hepaticum . . 362
Poultry and fish 362
Horseflesh . 363
Sausages, pork-pies, meat-pies, brawn, &c 364
Eggs .366
CHAPTER IX. Spirits 370
CONTENTS. XV
PAGE.
Vinegar ... . 372
Pepper • • • 375
CHAPTER X. Chicory . 380
Chocolate 384
Microscopical characters of coffee, chicory and cocoa . 386
CHAPTER XI. CHAPTER Xn
Preserved and tinned provisions 395
Colouring agents employed in food 400
CHAPTER XHI.
Poisons in foods 4°6
Phosphorus • . 4°?
Hydrocyanic acid ... . . . 408
Arsenic 4°9
The examination of wall-papers, &c., for arsenic . . . 410
Appendix To Food Examination
The sale of Food and Drugs Act, 1875 413
The sale of Food and Drugs Amendment Act, 1879 . . . 417
The Margarine Act, 1887 4x9
The sale of Horseflesh, &c.. Regulation Act, 1889 . . 420
Aerated waters .... 422
XVI LABORATORY WORK.
Part VI
Methods employed in Bacteriological Research, with special reference to the examination of Air, Water and Food. By Rubert Boyce, M.B.
Chapter I. Taob
Means of avoiding contamination 433
The nutrient media 434
Vessels used for storing nutrient media 441
CHAPTER n.
The methods of cultivation 444'
Inoculation of media . . ..... 444
Incubators 445
Drop cultures 447
Inoculation of animals and their post-mortem examination . 448
CHAPTER HI.
Methods of examination ... .... 451
Staining for micro-organisms 451
Cover-slip preparations 45^
Section cutting and staining ijc
CHAPTER IV.
The bacteriological examination of air 457
The bacteriological examination of water 460
The bacteriological examination of soil ..... 461
Anaerobic micro-organisms 4Q2
CONTENTS.
XVll
CHAPTER V.
General morphology and biology
PAGE.
CHAPTER VI.
The infective processes in man and animals . . . 474
Diphtheria ....
• 475
Pneumonia ....
• 475
Pleuro-pneumonia
Typhoid ....
. 476
Cholera ....
Chicken cholera .
. . . 478
Pig cholera ....
. . 478
Glanders
■ 479
Anthrax ....
• 479
Tuberculosis
Actinomycosis
ERRATA.
Page 49, line 30, for " Organic pollution," read " Some forms of
animal organic pollution — as by urine." Page 60, line \,for " liberated," read "induced to separate." Page 62, lines ig and i'i,for " iodide," read " iodine." Page 63, line 'S.'j,for "i.e., i milligramme of oxygen will be consumed," read " containing i milligramme of available oxygen." Page 73, line 30, for " 7," read " 07." Page 77, line 10, for " the most reliable," read " next to the meta-
phenylenediamine process the most reliable." Page 104, the first paragraph refers only to the non-poisonous metals. Page 120, line 18, for "would also be precipitated," read "would
also be, in part, precipitated."
Page 319, line 3, for " alum," read "alumina." Page 323, line 28, for " alum," read " alumina." Page 324, lines i, 7, 9 and 11, for " alum," read " alumina." Page 352, line 22, and page 396, line 4, for " crystallized," read " crystallizable."
PUBLIC HEALTH LABORATORY WORK.
Part I. The Hygienic Analysis Of Water
The object of a hygienic analysis of any water is, to learn whether the use of such for drinking purposes should be sanctioned or condemned from a health stand-point.
CHAPTER I.
If it is desired to fit up a laboratory to meet all the requirements of a hygienic analysis of water, it will be necessary to provide in the first place a bench, at least six feet long and two feet broad, standing to half the height of the operator, and placed in a good light ; this must be fitted up at the back with shelves, to carry some at least of the chemical reagents, i.e., those which are in most common use. By the side of the bench there should be a tap (furnishing a good supply of pure water), with, if possible, a small water sink beneath it. There must be gas in the room, but not necessarily near the bench, for it can be readily conducted thereto by tubing. A Bunsen gas burner is required, and it is
B very desirable to have two of these, so that both can be utiHsed at the same time. The Bunsen burner (fig. i) consists of a larger external tube surrounding a smaller gas-delivering one at its base, the former being perforated for the admittance of air — so that at the top the gas escapes well mixed with air, and hence oxidation (and therefore heat) in the flame is increased.
The apparatus required: —
I. A pair of balances with weights. Oertling's No. 3 (Townson and Mercer's Catalogue) will be found to be extremely suitable to all purposes. As shown in the accompanying diagram, they consist of a twelve inch
Fig. I. — The Bunsen burner.
beam which supports two pans, the ends of the beam being constructed with straight knife edges upon which the pans are suspended by agate planes. The case is fitted with a sliding window in front, which can be closed and still admit of the scales being made to register by means of a screw which projects externally.
The operation of weighing consists of first lifting the beam off its support by means of the screw, and then noting by the long indicator which hangs down in front of the central vertical support of the balances — and which must come to rest in an absolutely central and vertical positipu—whether the two pans exactly coun-
HYGIENIC ANALYSIS OF WATER. 3
terbalance each other ; if not the balance must be adjusted by means of a small mechanism situated on the top of the centre of the cross-beam and which can be moved horizontally to the right or left according as it is necessary to increase the weight in either of these directions.
The material is then placed upon the tray to the left, and the weights are added to the tray on the right.
FiQ. 2. — Chemical balances.
After the addition of each successive accretion of weight the result must of course be tested, but before any further addition or removal is made the scales must be brought to rest upon their supports, or the apparatus may be put out of gear.
Each of the weights is marked, as the plan of the
B2 box will best show (fig. 4). The larger brass weights representing grammes, the next in size decigrammes, the next centigrammes, and small forceps are used for picking up and applying them to the pan. The milligrammes-are added by a little piece of bent wire, which is carried by means of a sliding rod moving just above
Fig. 3. — Box of chemical weights.
the level of one of the cross-beams, which latter will be observed to show ten markings numbered from one to ten. By sliding the rod which supports the bent wire up to, say the marking No. 5, and then turning it
Fig. 4.— Plan showing the arrangement of the weights in box.
round by means of a screw, the wire may be made to ride upon that number, and the carrier can subsequently be withdrawn ; five milligrammes of weight will then have been added to that side of the scales.
HYGIENIC ANALYSIS OF WATER. 5
Example. — A small platinum dish is placed on that pan which is not surmounted by the apparatus for applying milligramme weights.
A five gramme weight is placed on the other pan.
The pans are lifted by means of the screw, and the platinum dish is found to weigh down the five grammes.
The scales are put at rest and a two gramme weight is added to the five, and this is also carried up by the superior weight of the platinum dish.
Another one grm. is added, and this is found to be too much, and is therefore removed, and a five decigramme weight {i.e., ^ grm.) substituted.
The platinum dish is still slightly the heavier, therefore another decigramme is added, with the result that the weights now slightly overbalance the dish.
The one decigramme weight is therefore removed and five centigramme substituted — not enough !
A two centigramme weight further added, however, so extremely nearly establishes the required equilibrium that the addition of another centigramme over-reaches the mark.
Three milligrammes are ultimately found necessary to effect such an uniformity between the weights of the contents of the two pans, that the index rests absolutely in a central and vertical position.
The weight therefore of the platinum dish is : — Seven grammes = 7
Five decigrammes = 0-5 Seven centigrammes = 0*07 Three milligrammes = 0-003
Total = 7"573 grammes.
2. A platinum dish, capable of holding a little over 100 c.c. of water.
3. Two shallow porcelain evaporating dishes, holding a little over 250 and 500 c.c. respectively (fig. 5)-
4. A porcelain crucible with cover, for igniting residues (fig. 6).
5. A white porcelain slab, about six inches by four.
6. Two white porcelain basins of about five inches diameter (fig. 7).
Fig. 5.— Evaporating dish. Fig. 6.— Crucible with lid.
7. A mortar and pestle (fig. 8).
8. Graham's or Liebig's condenser. Graham's will be found a most convenient instrument. As seen by figure 25, it consists of a smaller glass tube bent at one end, where it carries an indiarubber cork. Surrounding this smaller tube for about three-fourths of its extent is a larger one, closed at both ends by indiarubber corks, the centres of which are perforated for the
Fig. 7. — Porcelain dish. Fio. 8. — Pestle and mortar.
passage of the smaller tube. Cold water is made to circulate constantly in this outer tube by means of the tubing which connects its interior with the tap, the water escaping at the opposite end through the tubing which conducts to the sink. The cool water thus constantly kept circulating condenses the
HYGIENIC ANALYSIS OF WATER. 7
vapour in the inner tube, at the further extremity of which the condensed vapour finds its outlet and is collected.
A condensing apparatus can be readily improvised, but since either Graham's or Liebig's instruments are cheap (involving the outlay of only a few shillings !) and at the same time are less liable to leak, yield impurities, or to get out of repair, it is better and cheaper to purchase one of these.
9. A set (" nest ") of glass beakers (fig. 9) and large watch glass covers for same.
Fig. 9. — Nest of beakers.
10. A bell glass cover.
11. Two boiling-flasks or retorts (of about a litre capacity), one of which is seen attached to the condenser in figure 25.
12. Glass stirring-rods.
13. A small glass-stoppered bottle (250 c.c.) for the soap test.
14,. Glass funnels for filtration, with wooden support (fig. 10).
15. Glass burettes holding ten cubic centimetres, and
graduated in c.c's., and one-tenth of c.c's., one of which
Hould be mounted upon a wn'"''°n stand and should
LABORATORY WORK.
Wf
Fig. io. — Filtering apparatus.
be stoppered at the top, and fitted with a stop-cock at the bottom (fig. ii).
Fig. II. — Graduated burette with stopcock.
HYGIENIC ANALYSIS OF WATER. Q
i6. Four graduated glass-flasks ("measuring flasks") marked respectively at the height to which i, i, i and
Fig. 12. — Measuring flask.
j^ of a litre of water will stand. Figure 12 shows one such flask.
17. Six Nessler glasses, four of which are shown in figure 25.
18. A dozen test-tubes, with stand for same, and a test-tube cleaner and holder (fig. 13).
Fig. 13. — Test-tube stand, cleaner, and holder.
19. A glass pipette.
20. Two four-footed iron stands.
21. Two iron tripods (fig. 14).
22. Triangles of iron-wire lined with pipe-clay (fig. 15).
23. Wire gauze, cut about four inches square.
lO
24. A pair of small crucible tongs (fig. i5).
25. A small copper water bath, of about six inches diameter, and fitted with rings, which adapt its mouth
-Iron tripod.
so as to fit different sized evaporating dishes (fig. 17) ; or the water-bath recommended by the writer, which
Fig. 16. — Crucible tongs.
comes in equally serviceable for other analyses — apart from that of water. This consists, as in figure 18, of a
III 9
T
Fig. 17. — Ring water bath.
Fig. 18.— The form of water-bath recommended.
water bath of the common shape, but in its roof are three openings, a large central and two . small lateral ones.
HYGIENIC ANALYSIS OF WATER. II
A water bath is a receptacle in which the water it holds may be heated up to a certain temperature ; when vessels containing liquids are made to stand in or over ' the water thus heated, evaporation of their fluid contents may be effected at a temperature which must in any case be considerably below that which would be reached by the application of the naked flame.
26. A water oven. This is a small chamber whose double walls enclose water, which is made to regulate its internal temperature. The residue procured from the evaporation of a liquid over the water bath will still
Fig. ig.— a water-bath improvised Fig. 20. — A water oven, from an ordinary beaker.
contain a trace of moisture, it is therefore subsequently transferred to the oven, where absolute drying can be effected (fig. 20).
27. A packet of Swedish filter papers.
28. A long tube of thin colourless glass, known as " the two foot tube," employed in judging some of the physical characters of water.
29. A box of test papers, red and blue litmus and lead papers.
30. A long thermometer graduated in Fahrenheit degrees.
31. Indiarubber corks (perforated and imperforated) to fit the boiling flasks.
32. A " desiccator." A desiccator is simply a glass shade inside of which there is a vessel containing some
Fig. 21. — A desiccator.
agent which will keep the air free from moisture (such as strong sulphuric acid). A residue completely dried by heat will otherwise absorb a little of the vapour from the atmosphere while cooling, and thus increase slightly in weight (fig. 21).
Fig. 22. — A conical sediment glass.
33. A conical sediment glass (fig. 22).
The reagents required consist of :—
1. Distilled water.
2. Distilled ammonia-free water.
HYGIENIC ANALYSIS OF WATER. I3
3. Standard solutions oi : —
Chloride of ammonium.
Nitrate of silver.
Soap.
Nitrite of potassium.
Calcium carbonate.
Permanganate of potassium.
Sulphate of copper.
Sulphate of zinc.
Acetate of lead.
Protosulphate of iron.
Iodide of potassium.
Starch.
Hyposulphite of sodium.
Solutions of: — Alkaline permanganate. Potassium chroniate.
Pure and dilute sulphuric, ni- Potassium iodide.
trie, and hydrochloric acids. Potassium ferrocyanide. Liquor ammoniae. Potassium ferricyanide.
Chloride of ammonium. Pure soda.
Oxalate of ammonia. Sodium phosphate.
Ammonium sulphide. Nitro-prusside of sodium.
Ammonium molybdate. Chloride of barium.
Sulphuretted hydrogen. Brucine.
Silver nitrate. Starch.
Meta-phenylene-diamine. Perchloride of mercury.
Caustic potash. Nessler's reagent.
4. Zinc foil and copper-turnings.
The Weights and Measures upon the Metrical System.
(A knowledge of which is necessary for water analysis).
Length.
The metrical system is founded upon the " metre " which is divided and multiplied by ten to represent different measures as follows : —
I millimetre = xihru P^'^^ °^ ^ metre.
I centimetre = ^-J^ „ ,,
1 decimetre ^yu » »
I metre = 39*37 inches.
I decametre = 10 metres.
I hectometre = 100 , ,,
I kilometre* = 1000 „
Capacity.
1 centimetre cubed = o'o6i cubic inches. 28-35 )> » = I fluid ounce.
1000 „ „ or I cubic decimetre = i litre,
1000 litres = I cubic metre.
Weight.
I cubic centimetre of distilled water at 4° C, and 760 millimetres barometric pressure, weighs i gramme, which is the standard of weight.
I milligramme = ^^ part of a gramme.
I centigramme =^
I decigramme = ^
• The Latin prefix therefore indicates division, the Greek multiplication.
HYGIENIC ANALYSIS OF WATER. 1 5
I gramme = i5"432 grains.
I decagramme = lo grammes.
I hectogramme = loo ,,
I kilogramme = looo „
lib avoirdupois = 453*5 „ 1 gallon of water = 70,000 grains.
The term " septem " is sometimes used. It simply implies 7 grains.
Thermometer Scales.
Centigrade Freezing point = o Boiling point = 100
Reaumur „ „ =z o ,, „ = 80
.•. Centigrade Reaumur Fahrenheit — 32.
5 4 9
.•. To convert Centigrade to Fahr. x 9-5-5 and add 32.
„ „ Fahr. to Centigrade subtract 32 and -5-9x5. „ „ R6aumur to Fahr. -h 4 X 9 and add 32.
Table of Atomic Weights.
Barium
(Ba)
=
Calcium
(Ca)
=
(CI)
35-5
Copper
(Cu)
=
63-4
Iron
(Fe)
=
Lead
(Pb)
=
Magnesium
(Mg)
=
Hydrogen
=
I
= z=
Sodium
(Na)
=
Sulphur
=
Zinc
(Zn)
i6
LABORATORY WORK.
Table of Solubilities. (Showing the salts which are soluble in cold water).
Chlorides. — Nearly all. Those of Bi, Sn and Sb are
only partially so (Pb chloride is soluble only in hot
water).
Chlorates. — All.
Iodides. — Nearly all. Pb iodide only in hot water. Sulphides. — Those of the alkalies and alkaline earths. Sulphates.— l>iea.r\y all. Ag and Hg sparingly so. Nitrates and Nitrites. — All (a few basic nitrates sparingly
so).
Phosphates. — Those of the alkalies. Carbonates. — The alkaline ones.
Silicates. — Those of Na and K.
Arseniates. — Those of the alkalies. Chromates. — Nearly all (exceptions = Pb, Ag, Hg, Ba and
Bi chromates).
A WATER REPORT. 1 7
CHAPTER II. A Water Report
For hygienic purposes such a report must include all the information which can be obtained regarding the extent to which organic matter at present exists ; the evidence of former pollution by this material in the oxidised, &c., products of its decomposition ; and the amount to which poisonous metals — if any — are present. Much unnecessary confusion is created by the fact that no fixed terms are recognised and adopted by which results may be universally expressed. The results in the several steps of the analysis are, in consequence, variously returned by different analysts in terms of: —
Grains per gallon.
It seems most desirable, therefore, that some decision should be come to upon this point. Undoubtedly the best amount for working purposes in many of the stages of the analysis is 100 c.c. of the water, and the result, if this quantity be taken, can generally be at once expressed in " parts per 100,000 " (since 100 c.c = 100,000 milligrammes) ; this is by far the most common term employed in this country, and it is moreover
c in general use in France and Germany. In the estimation of organic matter, however, it seems preferable — dealing as we are with such small amounts — in order that the results shall represent whole numbers, to take larger quantities of the water, and to return the estimations as parts per hundred million. The findings of the whole analysis will then be appropriately expressed in terms of either parts per hundred thousand or parts per hundred million.
It appears advisable, nevertheless, to make one exception in the case of a quantitative examination of the poisonous metals, and to express these — in those uncommon cases where they exist — in terms of grains per gallon, since they are almost invariably thus referred to in this country.
Such then will be the quantitative expressions used throughout this book. Where, however, the terms employed are other than those to which the reader has grown familiar, he should convert them into such before attempting to form an opinion of the water. The process is a very simple one ! Parts per million are obviously converted into parts per loo million by multiplying by 100, or by moving a decimal point two places to the right, and parts per hundred thousand are converted into parts per million by multiplying by ten ; but the conversion of grains per gallon to parts per 100,000 is not so apparent.
Supposing a report reads " chlorine 2-8 grs. per galon," how many parts per 100,000 will this represent ?
Now there are 70,000 grains in a gallon.
>i .. 2-8 grains in 70,000 grains, or 2-8 parts per 70,000 parts.
A WATER REPORT. IQ
It is thus seen that it is only necessary to multiply results returned in " grains per gallon " by lo and to divide by 7, in order to convert them into " parts per 100,000," since grains per gallon are parts per 70,000. The converse of this also applies of course, and if it be desired to convert " parts per 100,000" to "grains per gallon " the returns must be multiplied by 7 and divided by 10.
Where the results of a quantitative test — as in the case of poisonous metals — are to be returned in terms of " grains per gallon " it is convenient to measure out 70 c.c. of the sample and to work with this. The reason for this is, that 70 c.c. represent " a miniature gallon " so-called, and the results can at once be expressed in terms of an imperial gallon. The relation between the so-called "miniature gallon" and the imperial gallon depend upon the following facts : —
1 c.c. of water weighs one gramme.
Therefore 70 c.c. ("in the miniature gallon") of water weighs 70 grammes or 70,000 milligrammes.
But I gallon of water weighs 70,000 grains.
Therefore since there are 70,000 component parts in either case (of milligrammes in one and grains in the other), the 70,000 milligrammes ihay be taken to represent " a miniature gallon," in which the grains of the imperial measure are represented by these milligrammes. The results arrived at in milligrammes, where 70 c.c. of water are taken, can therefore be at once expressed in terms of " grains per gallon." Thus it is seen that no calculation becomes necessary, and where the results are expressed in " grains per gallon " the " miniature gallon " may be advantageously chosen.
Subjoined is a copy of the Report in use at the Hygienic Laboratory, University College.
c 2
The Hygienic Laboratory,
University College, W.C.
Report on analysis of sample of water received on
from
Name or number of Sample
Date of Collection
Physical Characters
Reaction
Saline (or " Free ") Ammonia \
Organic (or " Albuminoid ") Ammonia j j
Oxygen absorbed from Permanganate in one hour (
(6) Fixed
(Jb) Permanent ....... . .
Equivalent to common salt
Nitrogen as Nitrates and Nitrites
Poisonous metals Grains per gallon
Microscopical Examination of the Sediment ...
Remarks
Date of examination. Signed
Parts per hundred thousand.
COLLECTION OF SAMPLES. 21
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