Per cent. alcohol by weight.

Temperature.

10°

15°

20°

25°

30°

35°

40°

45

0.93226

0.92852

0.92472

0.92085

0.91692

0.91291

0.90884

46

017

640

257

0.91868

472

069

660

47

0.92806

426

041

649

250

0.90845

434

48

593

211

0.91823

429

028

621

207

49

379

0.91995

604

208

0.90805

396

0.89979

50

0.92162

0.91776

0.91384

0.90985

0.90580

0.90168

0.89750

51

0.91943

555

160

760

353

0.89940

519

52

723

333

0.90936

534

125

710

288

53

502

110

711

307

0.89896

479

056

54

279

0.90885

485

079

667

248

0.88823

55

055

659

258

0.89850

437

016

589

56

0.90831

433

031

621

206

0.88784

356

57

607

207

0.89803

392

0.88975

552

122

58

381

0.89980

574

162

744

319

0.87888

59

154

752

344

0.88931

512

085

653

60

0.89927

523

113

699

278

0.87851

417

61

698

293

0.88882

466

044

615

180

62

468

062

650

233

0.87809

379

0.86943

63

237

0.88830

417

0.87998

574

142

705

64

006

597

183

763

337

0.86905

466

65

0.88774

364

0.87948

527

100

667

227

66

541

130

713

291

0.86863

429

0.85987

67

308

0.87895

477

054

625

190

747

68

074

660

241

0.86817

387

0.85950

507

69

0.87839

424

004

579

148

710

266

70

602

187

0.86766

340

0.85908

470

025

71

365

0.86949

527

100

667

228

0.84783

72

127

710

287

0.85859

426

0.84986

540

73

0.86888

470

047

618

184

743

297

74

648

229

0.85806

376

0.84941

500

053

75

408

0.85988

564

134

698

257

0.83809

76

168

747

322

0.84891

455

013

564

77

0.85927

505

079

647

211

0.83768

319

78

685

262

0.84835

403

0.83965

523

074

79

442

018

590

158

720

277

0.82827

80

197

0.84772

344

0.83911

473

029

578

81

0.84950

525

096

664

224

0.82780

329

82

702

277

0.83848

415

0.82974

530

079

83

453

028

599

164

724

279

0.81828

84

203

0.83777

348

0.82913

473

027

576

85

0.83951

525

095

660

220

0.81774

322

86

697

271

0.82840

405

0.81965

519

067

87

441

014

583

148

708

262

0.80811

88

181

0.82754

323

0.81888

448

003

552

89

0.82919

492

062

626

186

0.80742

291

Density (in grams per c.c.) of mixtures of ethyl alcohol and water. . cont.

Per cent. alcohol by weight.

Temperature.

10°

15°

20°

25°

30°

35°

40°

90

0.82654

0.82227

0.81797

0.81362

0.80922

0.80478

0.80028

91

386

0.81959

529

094

655

211

0.79761

92

114

688

257

0.80823

384

0.79941

491

93

0.81839

413

0.80983

549

111

669

220

94

561

134

705

272

0.79835

393

0.78947

95

278

0.80852

424

0.79991

555

114

670

96

0.80991

566

138

706

271

0.78831

388

97

698

274

0.79846

415

0.78981

542

100

98

399

0.79975

547

117

684

247

0.77806

99

094

670

243

0.78814

382

0.77946

507

100

0.79784

360

0.78934

506

075

641

203

For examining very dilute alcohol solutions in the tropics, the following table of the "density" at 32.5° C. (= 90.5° F.) of solutions containing 0 to 1.6 per cent. of alcohol by weight, may be found useful. It is due to A. F. Joseph and W. N. Rae.1

Alcohol per cent.

by weight.

" Density "; gram per c.c.

at 32.5°.

Difference for

0..2 per cent.

0.0

0.99489

38

0.2

0.99451

40

0.4

0.99411

38

0.6

0.99373

36

0.8

0.99337

38

1.0

0.99299

38

1.2

0.99261

37

1.4

0.99224

38

1.6

0.99186

There are three methods in general use for expressing the percentage of alcohol in a liquid - (1) percentage of alcohol by weight, (2) percentage of alcohol by volume, and (3) percentage of proof spirit by volume. The first method is the best for scientific purposes, and in general for miscellaneous analytical work, where often alcohol is only one of several ingredients of a mixture the composition of which is required. But the second method is by far the most convenient when alcoholic beverages or spirituous medicines are concerned, and both in this country and on the Continent, when "percentage of alcohol" is stated in connection with wines, spirits, etc., percentage by volume is generally understood, unless the contrary is stated or obviously implied. To obtain percentage by weight it is necessary to take the specific gravity of the liquid examined, or to weigh the liquid out; and when obtained, the percentage by weight may be misleading unless used carefully. For example, two specimens of wine may contain identical amounts of alcohol per litre, but expressed as percentage by weight the quantities may be appreciably different one from the other, because one wine may be sweetened and the other not. The sweetened wine being heavier than the other, contains a smaller percentage of alcohol by weight, though a litre of each contains the same amount.

1 J. Soc. Chem. Ind., 1914, 33, 991.

Beverages and spirituous medicines being almost invariably used, measured, compared, and referred to in terms of their volumes, and being of widely different densities, a truer idea of their relative alcoholic contents is given by expressing the latter as percentage by volume rather than by weight.

For commercial and fiscal purposes in this country, however, "proof spirit" is the unit of volume for alcohol. That this is so is, from some points of view, a pity. The use of the term, and of its adjuncts "over proof" and "under proof," is confusing and cumbersome. But it has been so long in employment, and is so . much interwoven with trade practices, that a change to the simpler method of expressing alcoholic strength by means of alcohol percentage would undoubtedly cause serious inconvenience. It must be carefully borne in mind, however, that although "proof spirit" terminology is cumbersome, there is no loss of scientific precision in adopting a diluted alcohol as unit, instead of absolute alcohol, so long as the unit is properly defined. On the contrary, there is more accuracy, because the diluted alcohol can be defined by means of its specific gravity to any degree of precision required, whilst the exact specific gravity of absolute alcohol is a matter of some doubt. In this connection it is of interest to quote from a report made in 1833 by a Committee of the Royal Society, who had been asked by the Treasury to advise them on the subject of spirit valuation for fiscal purposes: -

"With regard to the substance alcohol, upon which the excise duty is to be levied, there appears to be no reason, either philosophical or practical, why it should be considered as absolute. A definite mixture of alcohol and water is as invariable in its value as absolute alcohol can be. It is also invariable in its nature, and can be more readily and with equal accuracy identified by that only quality or condition to which recourse can be had in practice, namely, specific gravity. A diluted alcohol is, therefore, that which is recommended by us as the only excisable substance."

The legal definition of " proof spirit " is given a little later on.