4 BULLETIN 1009, U. S. DEPARTMENT OF AGRICULTURE. 
manufacturer. One of the criteria for changing it is the increased 
weight of the bottle when bottles of a definite capacity are being 
blown. 
To assist him in keeping the weight of the bottles as accurate as pos- 
sible, the hand blower familiarizes himself with the weights of the 
bottles as he blows them and can at once adjust any tendencies 
toward overweight or underweight. In. the Wage Scale and Work- 
ing Eules of the Glass Bottle Blowers' Association the blower is 
continually cautioned to " Avork as close to weight given as possi- 
ble." Similar precautions are taken in blowing bottles by the ma- 
chine process. For the past 30 years at least. (1) (6), 1 the National 
Glass Bottle and Vial Manufacturers' Association, composed of 
manufacturers, and the Glass Bottle Blowers' Association, composed 
of blowers, have held annual conventions, where questions pertaining 
to their several interests are discussed and agreements made by 
which each party should be governed. The limit of variation in 
weights which would be permitted during the ensuing year has been 
one of the questions decided at these meetings. This point became 
of special importance after the passage of the Net Weight Amend- 
ment to the Federal Food and Drugs Act, March 3, 1913, when the 
food officials were also consulted. The variations agreed upon and 
adopted in 1914 have been readopted annually without change. The 
manufacturer has the privilege of rejecting bottles whose weights 
fall outside these allowable variations. They are used in this bulle- 
tin in calculating the maximum variation in the volume of bottled 
foods. 
To show the extent to which any allowable variation will be ap- 
plicable to all bottles, it is necessary to note that the variation in the 
weight of hand-blown bottles is greater than that of machine-blown 
bottles. While this is generally an accepted fact (7), it has been 
further verified by 27 sets of data collected in the course of these 
investigations, each containing measurements on 25 to 50 bottles of 
4, 8, and 12 ounce weights. It was found that the respective average 
deviations were 0.12, 0.24, and 0.37 ounce in hand-blown ware, and 
.0.03", 0.06, and 0.18 ounce in machine-blown ware. It is pertinent 
also to note that machine manufacture has had a steady growth. In 
1912 (2) 33 factories in the United States were equipped with bottle- 
blowing machines. In 1913 (2) 37 factories and in 1914 (5) 54 
factories, or 37 per cent of those in the United States, were so 
equipped. It has been estimated that 45 per cent of the bottles blown 
in 1917 (7, p. 129) and 60 per cent of those blown in 1918 2 were made 
by automatic machines. This steady growth, together with the fact 
1 Figures in parentheses throughout this bulletin refer to the bibliography on page 20. 
2 Bureau of Chemistry surveys, unpublished. 
