Ice cream did much to popularize ice cream recipes and make its consumption into a fashionable middle-class pursuit. She wrote four books: "Ices Plain and Fancy: The Book of Ices" (1885), "Mrs. A.B. Marshall's Book of Cookery" (1888), "Mrs. A.B. Marshall's Larger Cookery Book of Extra Recipes" (1891) and "Fancy Ices" (1894) and gave public lectures on cooking. She even suggested using liquid nitrogen to make ice cream. Ice cream soda was invented in the 1870s, adding to ice cream's popularity. The invention of this cold treat is attributed to American Robert Green in 1874, although there is no conclusive evidence to
Ice cream maker firm consistency. Some machines—such as certain lower-priced countertop models—require the resulting mixture to be frozen for additional time after churning is complete. Nancy Johnson patented the first hand-cranked model in 1843. She then sold the patent to William Young, who marketed the machine as the "Johnson Patent Ice-Cream Freezer". Hand-cranked machines' ice and salt mixture must be replenished to make a new batch of ice cream. Usually, rock salt is used. The salt causes the ice to melt and lowers the temperature in the process, below fresh water freezing, but the water does not freeze due to the salt content.